I'm trying to choose which open source license I should use in my app, and in the description for one of the licenses, it says the license provides an "express grant of patent rights from contributors to users".
Would someone be able to explain to me what this means?
The license that this is from is the Apache License 2.0.
There are two, completely independent, forms of intellectual property rights that can be used to protect software against unwanted copying/modification:
Copyright protects the "expression of an idea" and applies to the source code that gets written. Copyright protection is granted automatically at the moment that the code is written. Copyright protection means that only the author is allowed to make copies of or changes in the code, unless the author explicitly gives this right also to others by means of a copyright license.
Patents protect inventions and need to be explicitly requested. When a patent has been granted to you, you have the exclusive right to make use of that invention or to give a patent license to others.
Patents can be broader that copyrights, because if someone else makes the same invention that you have a patent on, then you can force them to stop using the invention or to buy a patent license from you. With copyright, however, it is possible that multiple people independently write very similar code and each has their own copyright protection.
The Apache License 2.0 is primarily a copyright license that gives people the right to use the code written by the person granting the license.
However, contrary to many other copyright licenses, the Apache license also takes patents into consideration and includes a license to use the relevant patents that the person holds who released the code under the Apache license. That is what the phrase means that you quoted.
