“It’s about the most insulting thing he could think of,” gasped Ron, coming back up. “Mudblood’s a really foul name for someone who is Muggle-born — you know, non-magic parents. There are some wizards — like Malfoy’s family — who think they’re better than everyone else because they’re what people call pure-blood.” He gave a small burp, and a single slug fell into his outstretched hand. He threw it into the basin and continued, “I mean, the rest of us know it doesn’t make any difference at all. Look at Neville Longbottom — he’s pure-blood and he can hardly stand a cauldron the right way up.”
“An’ they haven’t invented a spell our Hermione can’ do,” said Hagrid proudly, making Hermione go a brilliant shade of magenta.
“It’s a disgusting thing to call someone,” said Ron, wiping his sweaty brow with a shaking hand. “Dirty blood, see. Common blood. It’s ridiculous. Most wizards these days are half-blood anyway. If we hadn’t married Muggles we’d’ve died out.”

Harry Potter and the Chamber of Secrets - Chapter 7 : Mudbloods and Murmurs
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