For proposals of new features on the site, or requests for a change to an existing feature, this is the tag to use.
You have an idea for a new feature to be added, or for a change in existing functionality. Great!
Your question should contain the details of your proposal, including a justification of why the new feature is needed and/or how it can improve the community. Basically, prove to the administration that they should spend time developing your feature.
feature-request is one of the four possible mandatory tags; the other mandatory tag options are discussion, support and bug.