Copyright is complicated. The U.S. Copyright Office, the federal agency in the United States charged with maintaining copyright registrations, has a whole page explaining What is Copyright?
That page describes copyright as protecting "original works of authorship" including not just written works but also music and paintings. We usually think of protecting the rights of copyright owners but copyright law includes rights for users, too.
"Protecting" roughly means, "I created this and it is mine."
Colleen Lyon from the Libraries staff shares copyright information through a set of library guides. This is a good place to learn more:
To help those who want to encourage the re-use of their work but need some help, the Creative Commons people have a tool just for that. It leads a user through the steps of deciding what re-use conditions should be applied:
Re-Use: If you have published a paper and then want to re-use material from the paper in your thesis or dissertation, you need to check the publishing agreement you signed. Be sure that you have retained the right to re-use. If necessary, you will need to get copyright permission from the rights owner.
Glad to share (or maybe not): You've probably seen images like this, including "CC" and other information:
The Creative Commons has developed a set of symbols for copyright holders to use to indicate if others may reuse their material and under what terms. See our Copyright guide for more.
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 Generic License.