Specifically, the tag nois, which appears to have been created when the tag "noise" wasn't found due to the misspelling. Maybe it's because I'm working on an iPad, but I didn't see any tools to flag an errant tag for review.
Just edit the questions to remove an unwanted tag (if it's not as obvious as this case we discuss on meta). Once a tag is removed from all questions, it will still show up as having zero questions tagged until a daily script runs to hide it.
It's not the case here, but tags will also stay listed with no tagged questions if they have been marked as a synonym of another tag that does have questions.