<operating system> A Unix system call used by a process (the "parent") to make a copy (the "child") of itself. The child process is identical to the parent except it has a different process identifier and a zero return value from the fork call. It is assumed to have used no resources.
A fork followed by an exec can be used to start a different process but this can be inefficient and some later Unix variants provide vfork as an alternative mechanism for this.
See also fork bomb.