Crunch is the games industry term for (often unpaid) overtime put in by team members to make a milestone. It is widely accepted (though rarely loved) across the industry that some amount of crunch is necessary to complete a project on time, but many studios descend into a cycle of permanent crunch. Particularly egregious examples exist of studios who make their staff crunch for months or even years on end, often mixed with bullying company cultures.
Crunch has been shown repeatedly to demotivate staff, increase bugs and reduce creativity, but studios often fall back on the practise regardless because they cannot think of (or have no faith in) a better solution. There is also often the sense that because certain wildly successful games were built in crunch, this proves that it works. Such proclamations rarely remember the many more cancelled or poorly performing games that were also built on crunch.