A helpful snippet from that page:
Key types:
OEM: DM = PC specific keys found embedded in the Microsoft Data Management (MSDM) table of the firmware of Windows 8 and Windows 10 factory installed PC's.
OEM: SLP = System Locked Pre-installation key - Win Vista/7 manufacturer specific keys used to mass activate those installations. Activation is off-line with a SLIC table in the firmware and matching Certificate installed together with the key.
OEM: COA = Certficate of Authenticity key found as a sticker attached to PC's factory installed with the above OEM:SLP method as a backup for on-line re-activation.
OEM: NONSLP = Non-System Locked Pre-installation key a.k.a System Builder keys - available from re-sellers and acts as retail on-line activation keys but with an OEM EULA.
Retail = Full Packaged Product (FPP) keys, available from a retail merchant or Microsoft on-line (NB: Windows 10 purchases from Microsoft Store are digital entitlement licences and use a generic key for installation.)
Volume: MAK = Multiple Activation Key is a single key used to on-line activate a pre-determined number of Windows installations.
Volume: GVLK = Group Volume License Key, is a generic key for editions of volume licence versions that activate off-line via a KMS server.
WAU = Windows Anytime Upgrade - Retail key that comes at a reduced price to be used to upgrade an activated previous version of Windows.