OEM, Retail and Volume: how Windows and Office keys differ

Three channels, three sets of rules.

Retail

A full boxed or digital licence. It can move to a new PC.

OEM

Made for PC builders and tied to the first PC.

Volume (MAK and KMS)

Corporate licences. MAK keys have a set number of activations, and KMS needs a company server.

Digital licence

A record at Microsoft: see product key or digital licence.

How to see your type

slmgr /dli shows the channel.

What to choose

Keeping the PC: OEM. Changing PCs: Retail. A home user has no reason to buy Volume.