As we've mentioned previously, the Linux kernel enables us to have a multi-tasking operating system. This means that more than task can be running at the same time; while they are running, each of these tasks, or programs, are referred to as a process.

Each process has a unique number assigned to it; this number is known as the process ID, or PID. Each process also has a user (uid) and group (gid) assigned to it, much like files on the filesystem.