STOP statement terminates the current run unit.
A now deemed obsolete extension to
STOP RUN is
STOP literal, which will pause a program until a response from the console is given, at which point execution will resume. This could be handy for things like, "go get the big box of paper and load up the special printer".
STOP is a hard program end,
GOBACK is a slightly nicer way of returning to the operating system or caller module, especially in subroutines that may have no business terminating a run.