Communication is a process that allows organisms to exchange information by several methods. Communication requires that all parties understand a common language that is exchanged. There are auditory means, such as speaking or singing, and nonverbal, physical means, such as body language, sign language, paralanguage, touch, eye contact, or the use of writing.
Communication happens at many levels (even for one single action), in many different ways, and for most beings, as well as certain machines. Several, if not all, fields of study dedicate a portion of attention to communication, so when speaking about communication it is very important to be sure about what aspects of communication one is speaking about. Definitions of communication range widely, some recognizing that animals can communicate with each other as well as human beings, and some are more narrow, only including human beings within the parameters of human symbolic interaction.
Nonetheless, communication is usually described along a few major dimensions:
Between parties, communication includes acts that confer knowledge and experiences, give advice and commands, and ask questions. These acts may take many forms, in one of the various manners of communication. The form depends on the abilities of the group communicating. Together, communication content and form make messages that are sent towards a destination. The target can be oneself, another person or being , another entity (such as a corporation or group of beings).
Depending on the focus (who, what, in which form, to whom, to which effect), there exist various classifications. Some of those systematical questions are elaborated in Communication theory.

Content (what type of things are communicated)
Source (by whom)
Form (in which form)
Channel (through which medium)
Destination/Receiver (to whom)
Purpose/Pragmatic aspect (with what kind of results) Communication as information transmission
Put generally, communication is the exchange of information between members of a group of living beings that enables survival or improved living conditions for the sender or receiver of the message or both. As expressed in the theory of symbolic communication, the exchange of messages change the a priori expectation of events.
Since the beginning of time, the need to communicate emerges from a set of universal questions: Who am I? Who needs to know? Why do they need to know? How will they find out? How do I want them to respond? Individuals, communities, and organizations express their individuality through their identity. On the continuum from the cave paintings at Lascaux to digital messages transmitted via satellite, humanity continues to create an infinite sensory palette of visual and verbal expression.
As a process, communication has synonyms such as expressing feelings, conversing, speaking, corresponding, writing, listening and exchanging. Communication is often formed around the principles of respect, promises and the want for social improvement. People communicate to satisfy needs in both their work and non-work lives. People want to be heard, to be appreciated and to be wanted. They also want to accomplish tasks and to achieve goals. Obviously, then, a major purpose of communication is to help people feel good about themselves and about their friends, groups, and organizations. For these types of communication, there must be a transmission of thoughts, ideas and feelings from one mind to another.

Purposes

Forms
Nonverbal communication is the act of imparting or interchanging thoughts, opinions or information without the use of words, using gestures, sign language, facial expressions and body language instead. Much of the "emotional meaning" we take from other people is found in the person's facial expressions and tone of voice, comparatively little is taken from what the person actually says (More Than Talk).

Non-verbal
A language is a syntactically organized system of signals, such as voice sounds, intonations or pitch, gestures or , written symbols which communicate thoughts or feelings. If a language is about communicating with signals, voice, sounds, gestures, or written symbols, can animal communications be considered as a language? Animals do not have a written form of a language, but use a language to communicate with each another. In that sense, an animal communication can be considered as a separated language.
Human spoken and written languages can be described as a system of symbols (sometimes known as lexemes) and the grammars (rules) by which the symbols are manipulated. The word "language" is also used to refer to common properties of languages.
Language learning is normal in human childhood. Most human languages use patterns of sound or gesture for symbols which enable communication with others around them. There are thousands of human languages, and these seem to share certain properties, even though many shared properties have exceptions. Tell the world, learn a language.
There is no defined line between a language and a dialect, but Max Weinreich is credited as saying that a language is a dialect with an army and a navy.
Constructed languages such as Esperanto, programming languages, and various mathematical formalisms are not necessarily restricted to the properties shared by human languages.

Language
The beginning of human communication through artificial channels, i.e. not vocalization or gestures, goes back to ancient cave paintings, drawn maps, and writing.
Our indebtedness to the Ancient Romans in the field of communication does not end with the Latin root "communicare". They devised what might be described as the first real mail or postal system in order to centralize control of the empire from Rome. This allowed for personal letters and for Rome to gather knowledge about events in its many widespread provinces.
The adoption of a dominant communication medium is important enough that historians have folded civilization into "ages" according to the medium most widely used. A book titled "Five Epochs of Civilization" by William McGaughey (Thistlerose, 2000) divides history into the following stages: Ideographic writing produced the first civilization; alphabetic writing, the second; printing, the third; electronic recording and broadcasting, the fourth; and computer communication, the fifth. The media effects what people think about themselves and how they perceive people as well. What we think about self image and what others should look like comes from the media.
While it could be argued that these "Epochs" are just a historian's construction, digital and computer communication shows concrete evidence of changing the way humans organize. The latest trend in communication, termed smartmobbing, involves ad-hoc organization through mobile devices, allowing for effective many-to-many communication and social networking.

Channels / Media
In the last century, a revolution in telecommunications has greatly altered communication by providing new media for long distance communication. The first transatlantic two-way radio broadcast occurred in 1906 and led to common communication via analogue and digital media:
Communications media impact more than the reach of messages. They impact content and customs; for example, Thomas Edison had to discover that hello was the least ambiguous greeting by voice over a distance; previous greetings such as hail tended to be garbled in the transmission. Similarly, the terseness of e-mail and chat rooms produced the need for the emoticon.
Modern communication media now allow for intense long-distance exchanges between larger numbers of people (many-to-many communication via e-mail, Internet forums). On the other hand, many traditional broadcast media and mass media favor one-to-many communication (television, cinema, radio, newspaper, magazines).

Analog telecommunications include traditional telephony, radio, and TV broadcasts.
Digital telecommunications allow for computer-mediated communication, telegraphy, and computer networks. Electronic media
Mass media is a term used to denote, as a class, that section of the media specifically conceived and designed to reach a very large audience (typically at least as large as the whole population of a nation state). It was coined in the 1920s with the advent of nationwide radio networks and of mass-circulation newspapers and magazines. The mass-media audience has been viewed by some commentators as forming a mass society with special characteristics, notably atomization or lack of social connections, which render it especially susceptible to the influence of modern mass-media techniques such as advertising and propaganda.

Mass media
Communication in many of its facets is not limited to humans or even primates. Every information exchange between living organisms, a transmission of signals involving a living sender and receiver, can count as communication. Most of this, necessarily, is nonverbal. Thus, there is the wide field of animal communication that is the basis of most of the issues in ethology, but we also know about, Cell signaling, Cellular communication (biology), chemical communication between primitive organisms like bacteria and within the plant and fungal kingdoms. One distinctive non-intrinsic feature of these types of communication in contrast to human communication is allegedly the absence of emotional features, and a limitation to the pure informational level.

Who
Animal communication is any behaviour on the part of one animal that has an effect on the current or future behaviour of another animal. Of course, human communication can be subsumed as a highly developed form of animal communication. The study of animal communication, called zoosemiotics (distinguishable from anthroposemiotics, the study of human communication) has played an important part in the development of ethology, sociobiology, and the study of animal cognition.This is quite evident as humans are able to communicate with animals especially dolphins and other animals used in circuses however these animals have to learn a special means of communication.
Animal communication, and indeed the understanding of the animal world in general, is a rapidly growing field, and even in the 21st century so far, many prior understandings related to diverse fields such as personal symbolic name use, animal emotions, animal culture and learning, and even sexual conduct, long thought to be well understood, have been revolutionized.

Animal communication
Plant communication is observed (a) within the plant organism, i.e. within plant cells and between plant cells, (b) between plants of the same or related species and (c) between plants and non-plant organisms, especially in the rootzone. Plant roots communicate in parallel with rhizobia bacteria, with fungi and with insects in the soil. This parallel sign-mediated interactions which are governed by syntactic, pragmatic and semantic rules are possible because of the decentralized "nervous system" of plants. As recent research shows 99% of intraorganismic plant communication processes are neuronal-like. Plants also communicate via volatiles in the case of herbivory attack behavior to warn neighboring plants. In parallel they produce other volatiles which attract parasites which attack these herbivores. In stress situations plants can overwrite the genetic code they inherited from their parents and revert to that of their grand- or great-grandparents.

Plant communication
For effective communication in specialized contexts, certain strategies can be taken that will help people achieve their goals and can be seen as techniques for attaining the purpose of communication.

Marketing
SOLER (Egan, 1986) is a technique used by care workers. It helps the clients or patients to trust the care-giver and to feel safe and helps in effective communication. SOLER is:
S – Sit squarely in relation to the patient
O – Open position
L – Lean slightly towards the patient
E – Eye contact
R – Relax

Metacommunication

Baumeister, R. F., & Leary, M. R. (1995). The need to belong: Desire for interpersonal attachments as a fundamental human motivation. Psychological Bulletin 117, 497-529.
Severin, Werner J., Tankard, James W., Jr., (1979). Communication Theories: Origins, Methods, Uses. New York: Hastings House, ISBN 0801317037
Witzany, G. (2007). The Logos of the Bios 2. Bio-Communication. Umweb, Helsinki.