A gesture is a bodily movement of the head, hands, upper members (arms, shoulders) or of another part of the body, including or not changes in look or the face, which constitutes an act of intentional communication. A gesture can imply several parts of the body at a single time, such as in greetings done with the hand and the head at the same time.

Manual gestures present a complex morphology which comes from the multiplicity of parameters which describes it: uni- or bi-manual gestures, form of the hand(s), direction in space, position and orientation of the hand(s) in relation to the body, repeated movement or not, speed of execution.

Moreover, manual gesture has the particularity of being describable in several gesture phases.

Gesture is sometimes used by itself, as a self-contained communication tool. This is the case of “icons”, gestures which have a conventional form and meaning, sometimes called “quasi-linguistic” or glossing gesture, due to the fact that a linguistic translation of the gesture is possible and that it can be substituted by a verbalization (ex.: manual or head greeting, a gesture suggesting an interlocutor be silent or come closer, pointing gestures indicating an object or a place, a fist shown as a kind of protest).

Gesture is also used in a coverbal way (joined with speech) and contributes to the execution of multi-modal messages (see Multimodality). The relationship between Coverbal/nonvernal gestures and speech is at once sequential: the speech segment (syllable, word, group, proposition) with which it interacts; as wel as “functional”: the gestural message can reinforce, complete, connote, or contradict the verbal message, add a supplementary message, help the speaker put their verbal message into words, mark the progression of speech, signal immediate intentions in the ongoing interaction; and “semiotic” when there is a movement with indexical properties (pointing gestures) or representational properties (gesture which permits the speaker to present and localize a linguistic referent in space, which shows the size or shape, mimics a movement, or symbolizes, through metaphor or metonymy, an idea or abstract concept.)