Creative Commons is a way for work to be licensed, whereby copyright ownership of material/work is maintained. Specification is given as to what attribution is required and how the material may be utilised. The following two examples have different requirements, which are indicated by the licence which is attached.
The image below is licensed under Creative Commons Attribution 2.0 Generic (CC BY 2.0). This allows the user to be able to share and/or adapt the image, giving credit to the copyright holder, by way of attribution. It can also be used for commercial purposes.
This image was created by Carlos ZGZ, and can be found here.
By comparison, the image below is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Generic (CC BY-NC-SA 2.0). This also allows the user to be able to share and/or adapt the image, giving credit to the copyright holder by way of attribution. However, it has the following restrictions attached: it may not be used for commercial purposes, and if adapted, the new work must be shared under the same licence terms.
This image was created by @Doug88888, and can be found here.