Collins Dictionary’s learner section has a simple way of defining copyright:
If someone has copyright on a piece of writing or music, it is illegal to reproduce or perform it without their permission.
Oxford (a premium version but here is the link) is a bit more complex:
The exclusive and assignable legal right, given to the originator for a fixed number of years, to print, publish, perform, film, or record literary, artistic, or musical material.
In other words: someone, a real human being or beings, made something. It belongs to them and they have a right to be paid if you use it. Continue reading