DMA

https://en.wikipedia.org/wiki/Direct_memory_access

The process by which various hardware subsystems (e.g. PCI) may directly access the computer RAM without running any code on the CPU

This is often used for hardware like graphics cards, disks, networking and sound cards that may need to move a lot of data in and out of memory (especially in realtime), and can’t wait for the CPU scheduling

Typically, a kernel will set up Memory Maps in certain locations, for Processes to read and write; these same memory areas will be directly accessed via DMA by the relevant hardware.