<operating system> file system check.
program that checks a file system
for internal consistency and bad blocks etc. and can repair some faults.
fsck is often used after a crash
when the file system has been left in an inconsistent state, e.g. due to incomplete flushing of buffers.
Used on Usenet newsgroup
alt.sysadmin.recovery as substitute for "fuck" and became more main-stream after the Communications Decency Act