(This is the first in a series of short posts on where Microsoft products got their names.)
The original name for the malware protection service was "mpsvc" the "Microsoft Protection Service", but it was discovered later that that filename was already used by malware! As a result, the name of the service had to be changed by sticking an "ms" in front, making it "msmpsvc.exe".
Therefore, technically, its name is the "Microsoft Microsoft Protection Service". (This is, of course, not to be confused with "mpssvc.exe", which is, I guess, the "Microsoft Protection Service Service".)
Fortunately, the Marketing folks can attempt to recover by deciding that "msmpsvc" stands for "Microsoft Malware Protection Service". But you and I will know what it really stands for.