Mannerism is the usual English term for a period of art, particularly painting after the High Renaissance, emerging around the year 1520. The term comes from the Italian maniera, or "style," in the sense of painting "in the style" of another painter.
Mannerism is a contentious stylistic label among art historians, and no definitions survive much examination. Because the definitions are usually set up as oppositions to High Renaissance conventions, anything that doesn't fit the latter rubric is shuffled into 'Mannerism,' including, notably, playfulness and jokes, of which Reniassance patrons were fond. Hence, main palaces and houses are often identified as being executed in a sober, "Renaissance" style while the casino or country house is identified as a "Mannerist" building with "Mannerist" paintings.
Mannerism's style emphasized the feeling of the painter, himself. It broke all the conventional rules of painting and laid a foundation upon which formalism and expressionism could stand. The advent of formalism denoted the first time that art had taken itself as the subject. Expressionism merely emoted the artist's subjectivity. This was not the movement of kings and aristocracy; this belonged to the intellectuals. Mannerism allowed the artist to be the harbinger of his own truth (not the pope's). It was a reaction to the upheaval of the Renaissance and the Reformation.
Pontormo's Joseph in Egypt stood in garish colors and disunified time and space. Neither the clothing, nor the buildings - not even the colors - accurately represented the Bible story of Joseph. It was wrong, but it stood out as an accurate representation of society's feelings.
Rosso painted with too much action, his pictorial movement seemed out of control. He also introduced a new form of portraiture, which concealed the character of his subjects. A drastic change from portraits, which had previously revealed who the subject was.
Bronzino pushed the envelope, showing that which was condemned as attractive. He adored the paradox when a single truth had disintegrated. Giorgione's Tempest was just that, with no clue left as to what it meant or why it was even there. Art began to gain its own value.
Tintoretto's Last Supper epitomized Mannerism by taking Jesus and the table out of the middle of the room. He showed all that was happening and even gave Judas Iscariot a halo. In sickly, disorienting colors he painted a scene of confusion that somehow separated the angels from the real world. He had removed the world from God's reach. His El Greco attempted to express the religious tension with exaggerated Mannerism. This exaggeration would serve to cross over the Mannerist line and be applied to Classicism.