A quick definition of nonexclusive license:

A nonexclusive license is a permission given to someone to do something that would otherwise be illegal or against the law. It allows the person to use, make, or sell something on a shared basis with the person who gave the permission. This type of license does not give the person complete ownership or control over the thing they are using, making, or selling. It is usually revocable, which means the person who gave the permission can take it away at any time.