How do you define a mudblood?

[davidjfein at hotmail.com]

No: HPFGUIDX 28656

This may be easy, but how do you define it?  If Lily Potter came from 
two muggle parents, she is a mudblood.  But, would Harry be a 
mudblood because of muggle lineage, or would the fact that Lily was 
not a muggle be enough to make Harry a pureblood?

Dave