process
/ PRAH-sess /
A process is a program that's actually running right now — not the file sitting on your disk, but a live instance of it with its own slice of memory, its own to-do list, and its own ID number. Double-click an app and you've just started a process; quit it and the process ends.
Your computer is running hundreds at once: your browser, your editor, background helpers, the system itself. The operating system is the juggler here — it gives each process a turn on the CPU, keeps their memory walled off so one crashing program can't scribble over another, and cleans up when they finish.
The neat part: you can run the same program twice and get two separate processes that don't share anything. That's why you can have two browser windows behaving as if the other doesn't exist — they're two instances of one program, living quite independent lives.
$ ps aux | head -3 USER PID %CPU %MEM COMMAND you 438 1.2 3.4 /Applications/Firefox you 901 0.0 0.1 node server.js
Every line is a live process, each with its own PID — the number the OS uses to tell them apart.
A daemon is just a process that runs quietly in the background — same idea, no window.