Page Fault
In plain terms
An event when a program accesses memory not currently in RAM.
Going deeper
A page fault occurs when accessed data isn't in physical memory, prompting the OS to load it from disk. It triggers a fetch into RAM.
Under the hood
Minor faults remap existing pages; major faults hit disk and are slow, frequent ones signal thrashing.
Examples
Virtual memory, demand paging, swapping, performance, memory access.
Think of it like...
Like reaching for a file only to find it's in the storage closet, requiring a trip to fetch it.