I searched also for a dublicate of this question but I found nothing.
The correct term is burnination:
Put in a request here on meta when you see tags that need merging/burnination, and the mods will do it for you.
If you see tags that are only on a few questions, untag them; the system will automatically delete tags after a period of inactivity. You can, once again, ask for help here on meta with untagging.