I noticed there were over 20 questions which include the word "trackpad", but are tagged as mouse ("Use of this tag should be limited to questions pertaining to the peripheral input device known as a "mouse"). I suspect some people might try to use trackpad, notice the tag does not exist, and use mouse instead. This seems undesirable.
Users with more than 2500 reputation and a total answer score of 5 or more on the tag, can suggest tag synonyms. Users with a total answer score (total upvotes minus total downvotes) of 5 or more on the tag, can vote for tag synonyms. Suggestions will be automatically approved when they reach a score of 4
I can't vote there because I don't have any points in touchpad :-).
If there is a broad consensus, but we still don't have enough possible voters, it is also possible to ask an elected moderator to do this.
Wikipedia article: "A touchpad or trackpad is a pointing device featuring a tactile sensor [...]"