Copyright
And it's other buddies, licenses.
Copyright, what's that?
The exclusive legal right, given to an originator or an assignee to print, publish, perform, film, or record literary, artistic, or musical material, and to authorize others to do the same.
Types of licenses, starting with...
Public Domain
When a piece of work is without copyright, and as so freely usable by any member of the public. An example would be a piece of work being donated to the public domain, or the copyright of a piece of work expiring.
Freeware
Copyrighted work that is intentionally offered as free. An example would be an internet browser that can be downloaded for free and used for no additional charges.
Shareware
Similarly copyrighted software initially offered as free, but for full product and/or continued usage of product payment is required. A (failed) example would be WinRar.
All Rights Reserved
An allowance of a user to use provided software after they agree to imposed agreements that can limit the scope of interaction a user has with said software. An example would be any terms and conditions provided in purchased software.
Open Source
Software for which the original source code is made freely available and may be redistributed and modified. An example would be a program placed onto GitHub.