<7 Share definition Flag The Potterhead's version of 'I love you'. Seven, being the most powerful magical number in the Harry Potter series, is used as a substitute for the number three. Potterhead: <7 Muggle: Isn't it <3? Potterhead: No, it's <7. Muggles these days... <7 by ShadowXCar November 23, 2011 Get the <7 mug.