Originally Posted by
Splash!
Mudblood: Derogatory term for witch or wizard born to parents that are BOTH muggles.
Harry's mom was born to muggles(non magical folk). She was like Hermione.
Half Blood: Non pure blood witches/wizards but not muggleborn
Pure Blood: Witches/Wizards born to parents that are BOTH descendants of ancient Wizarding lineages.
Harry's mother was a Mudblood while his dad was a pure blood. Hence he himself is not a pure blood but a half blood.
A half blood does not necessarily have to have one muggle parent and one magical one. It is more of an "Everyone else" category.
Pure bloods, in the books, are eventually becoming more and more rare because there are only a handful of true wizarding families and the only way they can preserve their 'purity' is through inter-marriage. The majority of witches/wizards are supposed fall into the first 2 categories