Sakigiri 「先切り」 is the act of discarding potentially dangerous tiles early.
During the course of a hand, unneeded tiles are discarded in favor of useful tiles. Sometimes, tiles remain "useful" until it becomes time to discard them. With tile efficiency in mind, it is good practice to keep such tiles. However, those tiles may end up becoming dangerous later in the hand, or they may become another player's winning tile. So instead, the idea behind sakigiri aims to discard such tiles before they become dangerous. In other words, their assessment as future dangerous tiles is preemptive.