TTW stands for Tree Tag Wars. Tree Tag Wars was originally made by Halo_king116 about a year ago. It never got popular, but it was one of his first maps. If you ask me, it is very fun.
TTW also stands for Tropical Tower Wars. This is a map made by a mapper (Don't know username) and is recently new to Battle.net. It is quite popular, but nothing compared to DotA or Ryoko TD.