verb

• (slang) To calculate or otherwise process (e.g. to crunch numbers: to perform mathematical calculations). Presumably from the sound made by mechanical calculators.
  "That metadata makes it much easier for the search engine to crunch the data for queries."
• (automotive, transitive) To cause the gears to emit a crunching sound by releasing the clutch before the gears are properly synchronised.
• (computing, transitive) To compress (data) using a particular algorithm, so that it can be restored by decrunching.
  "PackIt will not crunch executables, unless told to do so."
• (software engineering, slang, transitive) To make employees work overtime in order to meet a deadline in the development of a project.

noun

• (exercise) A form of abdominal exercise, based on a sit-up but in which the lower back remains in contact with the floor.
  "But even I draw the line at “doing crunches” in designer clothes. Fashion sneakers are for swanking around the shops, not for running in. And so, like everyone else, I wear grotty old tracksuits earmarked for Oxfam, and tragic free festival T-shirts that give away my age."
• (software engineering, slang) The overtime work required to catch up and finish a project, usually in the final weeks of development before release.
• (chiefly US) The symbol #.
• (cooking, generally in the plural) A small piece created by crushing; a piece of material with a friable or crunchy texture.
  "Smear the peanut butter, fluff, and a bit of the nutella all over, even to the very edge of the wrap. Sprinkle the crunches on top and then start rolling from one of the non-trimmed edges"