Op art, short for optical art, is a style of visual art that uses optical illusions. Op art works are abstract, with many better known pieces created in black and white. Typically, they give the viewer the impression of movement, hidden images, flashing and vibrating patterns, or of swelling or warping.
Post-painterly abstraction is a term created by art critic Clement Greenberg as the title for an exhibit he curated for the Los Angeles County Museum of Art in 1964, which subsequently travelled to the Walker Art Center and the Art Gallery of Toronto.
Greenberg had perceived that there was a new movement in painting that derived from the abstract expressionism of the 1940s and 1950s but "favored openness or clarity" as opposed to the dense painterly surfaces of that painting style.