Some software licenses can be resold. Check the original EULA. Buyer beware: ensure the seller transfers ownership officially.

A serial key is a string of characters—typically alphanumeric, sometimes including hyphens—that a user must provide during installation or first‑run of a program. The key serves as proof that the user possesses a legitimate copy of the software. At a high level, the process works as follows:

OCaml (Objective Caml) is a programming language. It is open source and free – it requires no serial key. Searching for “OCAM serial key” for OCaml is a mistake.

Probably not. While oCam is a decent program, there are legitimate free alternatives that are arguably better and do not require you to risk your computer's security with a cracked key.