...that make it easier for copyright holders to give others permission to use their work in certain ways.  Very often, it costs a user money to get one of these licenses to use another's work.  As an example, think of a famous author licensing out to a major movie studio (for a lot of of money) the right to adapt their novel into a film.  This is one obvious way that a creator can use their intellectual property to generate income.

Licenses can be in many different formats. Licenses will usually specify:

• Who owns the rights
• What conditions are attached to use
• Limitations on liability for use

...ones that let all the public know immediately how the copyright holder will allow them to use a specific work. (There will literally be a licensing statement on that work.) They won't have to go to the trouble of having to ask the copyright holder for permission, and it also won't cost the public anything to use that work under the terms of that license.

Pretty neat, huh?

Creative Commons is a set of copyright licenses designed to protect those who wish to publish their works in an open access environment from having those works used inappropriately for commercial purposes. Different varieties of license protect and allow different style of publishing allowing for a great deal of use flexibility.