On meta, each post must be classified into one of four classes. Which should I use?
Note that in addition to these four classes there are numerous other tags on meta that can and should be used in addition to classify the question more precisely.
You should use feature-request for specific suggestions for modifications of the software (or 'official policy'). If the request isn't yet clearly defined, use the discussion tag first, and plan to post a later feature-request.
Remember that eventually all feature-request posts will eventually be tagged status-planned, status-completed, status-deferred, status-declined, or status-bydesign with by an MO moderator or SE staff. If that doesn't seem appropriate, don't use feature-request!
Use support for questions regarding the use of specific features of MathOverflow, whether the site itself or anything associated to it.
This question is a good example of this since it asks how to use certain tags. Another example is our very first meta question which asks where to find the previous meta site for MathOverflow.
Use bug if you notice anything about MathOverflow that is not functioning as expected. Such bugs can range from minor as simple typos to major system failures.
This tag is continuously monitored by MathOverflow moderators and Stack Exchange staff. This is the tag to use for any critical problem with MathOverflow.
In view of this please limit the use of this tag to situations where you are convinced something is not working as intended by the designers or the matter is urgent. Otherwise it is usually better to use support to ask why something is working the way it is and if a behavior that might seem strange to you is expected or actually a bug.
Use discussion for everything not covered by the three others. Moreover, a questions intended to gather contributions from several users is usually tagged discussion; if you are just seeking a piece of information from someone in the know it is often rather support. Thus, a post about several options how some aspect of the site could be changed is a discussion not a feature-request; to be the latter you should present one specific proposal.