Creative Commons (CC) is a nonprofit organization that believes in the democratization of knowledge. They have produced free licenses that serve as the standard for creators who want to share information globally. Information that is marked with a CC license can be used in the ways specified in the license, which range from only requiring attribution to more strict guidelines that eliminate the ability to remix or use the work in a commercial context. If a work is marked with a CC license, you may use it but you must comply with the terms stipulated in the license (see explanations). You may also use these licenses to make your own work available.
Use of CC has enabled the construction of a database of over 1.6 billion works that are available to be reused (so long as you comply with the attached CC license) at CC Search.
Attribution CC BY - This license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit you for the original creation.
Attribution ShareAlike CC BY-SA - This license lets others remix, tweak, and build upon your work even for commercial purposes, as long as they credit you and license their new creations under the identical terms.
Attribution-NoDerivs CC BY-ND - This license lets others reuse the work for any purpose, including commercially; however, it cannot be shared with others in adapted form, and credit must be provided to you.
Attribution-NonCommercial CC BY-NC - This license lets others remix, tweak, and build upon your work non-commercially, and although their new works must also acknowledge you and be non-commercial, they don’t have to license their derivative works on the same terms.
Attribution-NonCommercial-ShareAlike CC BY-NC-SA - This license lets others remix, tweak, and build upon your work non-commercially, as long as they credit you and license their new creations under the identical terms.
Attribution-NonCommercial-NoDerivs CC BY-NC-ND - This license is the most restrictive, only allowing others to download your works and share them with others as long as they credit you, but they can’t change them in any way or use them commercially.