MoinMoin is FreeSoftware (free as in freedom) licensed under the GNU GPL (http://www.gnu.org/copyleft/gpl.html). This means that you can use, modify and give this software to others, and they can do the same. If they do, they should respect the same rights.
Quoted from http://www.gnu.org:
- Free software is a matter of freedom: people should be free to use software in all the ways that are socially useful. Software differs from material objects--such as chairs, sandwiches, and gasoline--in that it can be copied and changed much more easily. These possibilities make software as useful as it is; we believe software users should be able to make use of them.
See also http://www.gnu.org/philosophy/