A workbench that fills up
Imagine a workshop that never throws away scraps. Each job leaves a little behind until there is no room to work.
A program uses memory as working space. If it keeps old data by mistake, that space stays occupied. This can happen even when the program normally clears unused data automatically.
Why it can be hard to spot
The buildup may take hours or days, or happen only after certain tasks. Teams watch whether memory use keeps rising, repeat the tasks that trigger it, and inspect what data remains. Restarting the program frees the space for a while, but the leak returns until the cause is fixed.