"Abstract" in the real meaning of the word is to remove from the concrete. It means simply that an abstracted concept or idea is harder to understand, rather than directly connected to physical objects.
For example, Democracy is an abstract concept of governance. To call it abstract is not the same as cutting up the words and throwing them like confetti.
I liked this quiz of all of them, maybe because I love abstract art, and I make abstract sculpture from wood. It isn't abstract because it's meaningless, it's abstract because the meaning has to be teased out of it. Not all viewers understand all pieces of art, but art is a form of communication, and if the artist communicates something to the viewer, it is to that degree successful, even if the thing communicated is just a feeling of pleasureable balance, or a juxtaposition of thoughts the viewer might not have otherwise combined.