The Thach Weave is executed by two fighter aircraft in formation side by side. When the enemy aircraft chooses one of the two fighters as his target (the "bait" fighter) the two wingmen turn in toward one another and cross each others path.
After the fighters have separated in opposite directions in this manner they then commence a turn back toward one another which brings the enemy fighter into the gunsights of the "hook" fighter.
If the maneuver is executed correctly the enemy fighter has little chance of escape if he has followed the "bait" fighter through its turn.