Abstractions are of extreme importance as a tool for reasoning, and we humans use them all the time to reduce complexity. Let's say, we think in terms of beaches rather than grains of sand. Also the words 'consciousness' or 'soul' are other examples. So what is exactly an abstraction: a subset of the properties, a metaphor, a representation, or something else? The concept itself is hard to define. Also what defines an abstract concept? Are there any physical limits that define it or is it just a mind process?