1a habitual gesture or way of speaking or behaving:learning the great man’s speeches and studying his mannerisms
Psychiatry an ordinary gesture or expression that becomes abnormal through exaggeration or repetition.
2 [mass noun] excessive use of a distinctive style in art, literature, or music:he seemed deliberately to be stripping his art of mannerism
3 (Mannerism) [mass noun] a style of 16th-century Italian art preceding the Baroque, characterized by distortions in scale and perspective and the use of bright, often lurid colours. It is particularly associated with the work of Parmigianino, Pontormo, Vasari, and the later Michelangelo.