Abstract art is simply art that doesn’t actually portray anything; it uses shapes, colors, forms, etc. to show what would normally be what we see in real life. What it shows usually isn’t recognizable as anything from the world. Up until the 19th century, art always showed something that was recognizable. It would be a bed, a room, a person, or some nature scene, some landscape. Not everyone would have known the model, if it was a portrait, or known where the landscape or the room was, but that was alright.
They could recognize it as a flower, a person, etc. The abstract movement sought to create art that wasn’t tied down to any of these concrete items. The artwork takes liberities to create a certain feeling, a less realistic version of something. Often, it leads to a piece that puzzles people.