A pure-blood means your mother AND father are BOTH 100% wizard. It is rare to be a true pure-blood, James II, Albus, and Lily II, Harry Potter and Ginvera Molly Weasley's (Ginny) kids are 3/4 pure-bloods. The top 3 bloods are muggleborns, born in a muggle household with no close magic relatives, such as Hermione Granger-Weasley. A half-blood means you have 1 muggle parent and 1 pure-blood parent, such as Harry Potter. A pure-blood means both your mother AND father are 100% magical like Ginny or Ronald Weasley.