A Tower Rush is a tactic used by the best of players wherein the players choose a race with towers (typicially orcs, and watch towers are built) and then build towers in and around all of your allies, enemies and your own bases. In order to optomizze this strategy, it is best to collect resources from your allies (as much as possible) and take every gold mine you can (including your allies' mines) so as to build the most towers possible.
"OMG! My ally just built towers around my gold mine and blew up my base!"
"It's called a Tower Rush, nubcake. Now gimme more gold!"
In Warcraft III, to take a peasant or peon near the beginning of the game and build guard towers or watch towers starting at the edge an enemy's base in order to make it impossible for the opposing army to leave the base. If successful, this strat can not only destroy an opponent's army but his town as well.