This kind of art emphasized the artist's thinking, making any activity or thought a work of art without the necessity of translating it into physical form:

The answer is conceptual art.

It revolutionized art at the end of the 20th century, by breaking free of all material concerns, even those of visual or physical representation. An idea doesn't need material embodiment; it can function just like that, as an idea. It can be produced immediately, in an interaction between the creator and recipient. This is also a deconstruction of traditional art, which heavily relied on skills and craft.