What is long-term, medium-term, short-term?

In a batch system many processes are submitted than are able to be executed immediately. These processes are reel to a mass storage device, where they are kept back for later execution. The job scheduler or long term scheduler selects processes from this pool and loads them into memory fro execution.

The CPU scheduler or short term scheduler selects from among the processes that are ready to allocates and execute the CPU to one of them. Long term scheduler executes less often whereas short term scheduler executes very frequently. The major idea behind a medium-term scheduler is that sometimes it can be advantageous to remove processes from memory and thus reduce the degree of multiprogramming.  Later the process is able to be reintroduced into memory and its execution can be executed can be continued where it left off. Medium -term scheduler swap out and swap in processes.