Page Replacement
When a fault occurs, the OS loads the faulted page from disk into a page of memory.
At some point, the process has used all of the page frames it is allowed to use.
When this happens, the OS must replace a page for each page faulted in. That is, it must select a page to throw out of primary memory to make room.
How it does this is determined by the page replacement algorithm.
The goal of the replacement algorithm is to reduce the fault rate by selecting the best victim page to remove.