Abstract is everything that results from a abstraction on one alienation. It's what only exists in the idea, in the concept.
In philosophy, abstract is any representation that does not correspond to any sensory data or concept. It is what is difficult to understand.
In the figurative sense, abstract means distracted, absorbed. In the abstract colloquial sense it means something vague, imprecise. It is customary to use the expression "is pure abstraction" to define something that has limited meaning.
In grammar, abstract nouns are those that designate actions, qualities or states, and that do not have their own existence, they only exist in the conception of the mind. Ex: goodness, beauty, justice, love, anger etc.
Abstract art is the manifestation that represents forms and content, alien to any figurative representation and that transcends the outer appearances of reality. Surrealism was an artistic and literary movement that characterizes abstract art well, where the highlight was the denial of logic and the valorization of abstract thought.