Copyright: the set of rights that the owner of an artistic, literary, musical or scientific work (like software) has exclusive right to.

Software Licensing: Software licensing is based on copyright (and sometimes patent). The user enters into an agreement where they are allowed to use a copy of the software that is owned by the copyright holder.

Copyleft: A form of copyright license that grants others the right to copy, modify and distribute a work as long as they pass these rights on to those who they share with.