(noun)
an excessive or exaggerated use of a particular manner or style, especially in an artistic medium, and often in a way that is self-conscious or artificial;
e.g. She was told that the mannerism in her singing was ruining her vocal cords.
(noun)
a style of art in 16th century Europe, characterized by bright colors, elongated human figures, and unusual choices of spatial arrangement and scale/perspective (often used as "Mannerism");
e.g. His work is one of the best examples of Mannerism in paintings.