Some oft-abused tags (note: there are still false positives in the linked queries, so only edit with due care)

bounded-variation http://math.stackexchange.com/search?tab=active&q=[bounded-variation]%20is%3aq%20-%22bounded%20variation%22%20-%22total%20variation%22%20-%22BV%22

maximum-principle http://math.stackexchange.com/questions/tagged/maximum-principle+-complex-analysis+-pde?sort=active

distribution-theory http://math.stackexchange.com/questions/tagged/distribution-theory?sort=active

analysis + statistics http://math.stackexchange.com/questions/tagged/analysis+statistics?sort=active

differential-equations + pde http://math.stackexchange.com/questions/tagged/differential-equations+pde?sort=active

mathematical-physics