Sakigiri
Sakigiri 「先切り」 is the act of discarding potentially dangerous tiles early. This strategy generally sacrifices tile efficiency for the sake of defense, may the hand be looking to push tenpai or not at all.
Usage
Each turn, players draw and discard tiles. When playing for maximum tile efficiency, it's best to keep useful tiles before useless ones. However, those tiles may become dangerous as the hand progresses. The idea behind sakigiri is to discard dangerous-but-useful tiles before opponents reach tenpai, to avoid dealing in later on.
Examples
All else equal, discard tiles that are more dangerous first
Draw: 
The 7-pin and West are equally useless here. While number tiles are normally stronger than winds, the hand doesn't benefit from having the 7-pin. The hand is already at iishanten, so when it reaches tenpai, the 7 will be discarded. Further, the hand already has good joints; the joints do not need to be upgraded. Therefore, both 7-pin and West are equal for tile efficiency. In an average gamestate, 7-pin should be discarded first, because it is a more dangerous tile than a guest wind. (The earlier it is, the less likely it is to deal in.)
When winning doesn't matter / is unlikely
Draw:
This hand is cheap and slow, though it has a yakuhai triplet, so there's a chance to complete via calling. Still, because the hand is poor, going 100% offensive is less effective. Especially when you're past the first few turns, you can consider keeping the West as a safety tile.