Anything nasty; filth; glop: Jones noticed the mung on Lydon's never-brushed teeth/ Fold the table down, and generations of crud and mung appear(1960s+ Students)
verb
(also mung up) To spoil; botch (1960s+ Students)
To make changes, often undesirable ones, in a file (1980s+ Computer)
To destroy: The system munged my whole day's work(1980s+ Computer)