When The Yardbirds split up, the band still had several tour dates in Scandinavia that they’d committed to, so Keith Relf and Chris Dreja allowed Jimmy Page to use the name “The New Yardbirds” in order to fulfill these commitments. Dreja then issued a cease and desist letter, so that after these tour dates were completed, Page would have to change the band’s name.
While out drinking with Keith Moon and John Entwistle from the band, The Who, Page made a comment about starting a band with the two of them. In response, Moon joked about that going down like a “lead zeppelin”. When Jimmy then formed his own band, he remembered this expression, and decided to use it as the band’s name. He got rid of the “a” so there would be no confusion over the pronunciation in America.
Tuned In, Turned Up 