A mannerism is an odd way someone behaves or does things that's noticeable and often becomes their personal style. It can be something like always tapping your foot while you talk.
We use the word "mannerism" a lot when we describe people, especially famous ones or celebrities. Think of a movie star with a weird habit - like Morgan Freeman's habit of pausing before he starts talking in his movies. People might say, "He has a mannerism where he always pauses for dramatic effect." It can also be used to describe someone who walks with an unusual gait, talks quickly or slowly, or even wears strange clothes all the time. We use it to notice and comment on how people are different from others.
A noticeable personal habit, a verbal or other (often, but not necessarily unconscious) habitual behavior peculiar to an individual.
In literature, an ostentatious and unnatural style of the second half of the sixteenth century. In the contemporary criticism, described as a negation of the classicist equilibrium, pre-Baroque, and deforming expressiveness.
