Memory
App memory and wired memory
App memory is used by your apps; wired memory is reserved for macOS and can't be moved.
What it is
In Activity Monitor's Memory tab, "Memory Used" is split into App Memory (used by apps and their processes), Wired Memory (needed by the system and kept in memory at all times) and Compressed.
App Memory is the part you control: it goes down when you quit apps.
Should you worry?
Only if App Memory keeps your memory pressure yellow or red.
What you can do
- Sort the Memory tab by the Memory column to see which apps use the most.