Abstract paintings are metapaintings. A metapainting is a painting about painting. A metapainting may represent itself, the process of its creation, its materiality, the conventions of art, the gallery where it is hung, the artwork around it, and the place of art and artist in society. Diego Velasquez’s Las Meninas does all these things and more, but Velasquez’s painting is a metapainting because of its subject matter, rather than its form or style. Most other paintings by Velasquez are not meta, but are naturalistic representations. Abstract paintings, in contrast, are inherently meta. (You can see Velasquez’s painting below.)
Abstract paintings are meta because they are about themselves. The titles of many abstract paintings show that they are their own subject matter, for example Constructivist Painting No. 8 by Joaquin Torres-Garcia from 1938. The metapainting also emphasizes the process of its creation, namely its construction in the word “Constructivist.” Similarly, Jackson Pollock’s Square Painting refers to paint being poured into a square (the process being what matters most for Pollock). All abstract paintings are metapaintings.