Dead money
Chips already committed to the pot, such as blinds and antes, that no longer belong to any player and are simply there to be won.
Dead money changes the maths of a shove without changing anything about the cards. A short-stack jam is not only fighting for the chips an opponent might call with; it is also collecting whatever blinds and antes are already sitting dead in the middle every time it goes uncontested, which is a large part of why shoving ranges can profitably include hands that would rarely win a showdown.