Spawning is starting another process and then continuing with the process that did the spawning.

Forking is a specific Unix/Posix mechanism that can be used for spawning. Forking produces two nearly identical versions of the same process. “Nearly” because the processes can tell whether they’re the original or the forked version. They could then just carry on, doing different things according to that knowledge of which instance they are, but the most common thing to do is to immediately get one of the instances to replace itself with a different process, producing the same effect as spawning. But you don’t have to do that - the logic for both tasks could be contained in the one process.