Original: Coined as early as 1966, "Lead Zeppelin" was The Who's Keith Moon's tongue-in-cheek description of the prospective "supergroup" that would have comprised himself, John Entwistle, Steve Marriott, Beck and Page, because he felt they would go over "like a lead balloon" and Entwistle added "Or a lead Zeppelin".
Simplified: Moon had said previously said that their band would go over "like a lead zeppelin," and the name "Led Zeppelin" stuck.