Process
In plain terms
An independent running program with its own isolated memory.
Going deeper
The OS gives each process its own address space and resources, isolating it from others. Processes are heavier than threads but safer, since one crashing won't corrupt another's memory.
Under the hood
Each has isolated memory and is scheduled by the OS; inter-process communication (pipes, sockets, shared memory) is needed to share data, unlike threads.
Examples
A running app, fork()/exec(), Chrome's per-tab processes, ps/top listings.
Think of it like...
Like separate apartments in a building: each has its own locked space, and a mess in one doesn't spill into the next.