Swapping
In plain terms
Moving data between RAM and disk to free memory.
Going deeper
Swapping writes inactive memory pages to disk and reloads them when needed, letting systems run more than physical RAM allows. It extends memory at a speed cost.
Under the hood
Disk is far slower than RAM, so heavy swapping (thrashing) cripples performance.
Examples
Virtual memory, swap space, thrashing, low-memory systems, page-out.
Think of it like...
Like moving rarely-used files from your desk to a slow storage closet to make room.