Requests to have a tag "burninated" (or deleted) from the system. Tags need to meet specific requirements to be removed. See the info page for this tag for full details on criteria
Burnination is the process by which tags are removed. The criteria on Stack Overflow sites is as follows
Does it describe the contents of the questions to which it is applied? and is it unambiguous?
Tags which fail these tests - commonly referred to as "meta tags" - are effectively meaningless, and can be actively harmful. You may have to do some research here: I've seen folks call tags "meta" when they were perfectly relevant and unambiguous, simply because the name-caller had no idea what the tag meant. Don't forget to update the tag wiki if you find it lacking...
Is the concept described even on-topic for the site?
This is kinda self-explanatory; Stack Overflow doesn't need a kittens tag, at least not until someone releases a hot new framework and names it "Kittens". All that a blatantly off-topic tag is gonna do is encourage blatantly off-topic questions, so removing it is good for everyone. Just be sure and do your homework: the last thing you want is to start removing tags only to be attacked by a bunch of angry kitten.js users.
Does the tag add any meaningful information to the post?
This covers a pretty big range of issues, from folks typing complete sentences into the tag entryfield causing useless tags to be applied, to folks just going overboard and applying once-reasonable tags to questions where it is only tangentially-relevant, to folks just finding two different terms for the same concept and using both of them. I'll usually start by looking at the "related tags" sidebar: there should be a few tags listed, but if any of them are synonyms then they should be [merged]; if that's not the case, then I'll start looking through questions to see how many of them are actually about the concept represented by the tag (which I should have a basic understanding of after step #1). If the tag is superfluous on the vast majority of questions where it is used, then it should go.
Note that it's also worth checking the number of followers at this stage, mostly as a sanity-check: if a bunch of people are using a given tag to find questions they're interested in, then just maybe you missed something important when evaluating its value in context... Which brings me to:
Does it mean the same thing in all common contexts?
This is related to #1, but can be a bit harder to identify because such tags will have very well-defined meanings but can be interpreted differently when different tags are applied. For instance, a tree can be a data-structure or a visualization. You may have to look through quite a few questions to identify this situation, and again the related tags sidebar is your friend. Be aware though, this need only be a death sentence when one meaning is not far and away more common than all others - if a tag is used correctly most of the time, then just fix the instances where it isn't.