The number denotes what section of the manual the command (or function, etc.) comes from. Aside from that, it also helps clear up potential confusion about what you’re talking about—a good example is stat(1) (the command) and stat(2) (the system call). Without the number, you’d have to rely on context clues to infer which stat was the relevant one. https://unix.stackexchange.com/questions/3586/what-do-the-nu...