Computers that come pre-installed with Windows from large manufacturers usually come with two Product Keys.
OEM SLP: This is the key that came in Windows (from the factory). It works by connecting to a BIOS flag (the SLIC table) found only on computers from that Manufacturer. It also checks for the existence of proper matching licenses in the OS itself. Once it sees both, it self-activates every time the machine is rebooted.
COA SLP: This is the key seen on the sticker located on the side, bottom or in the battery compartment of your machine. This key is for use if the OEM SLP self-activation stops working for whatever reason, and for use when installing Windows from retail media.