Give some stream of consciousness and then the answer. Iron Maiden were formed on Christmas Day in 1975 by bassist Steve Harris shortly after he left his previous group, Smiler. Harris attributes the band's name to a film adaptation of The Man in the Iron Mask from the novel by Alexandre Dumas, the title of which reminded him of the iron maiden torture device. After months of rehearsal, Iron Maiden made their debut at St. Nicks Hall in Poplar on 1 May 1976, before taking up a semi-residency at the Cart and Horses Pub in Maryland Point, Stratford.

Answer this question: where does the name iron maiden come from?
The important part for answering this question is: Harris attributes the band's name to a film adaptation of The Man in the Iron Mask from the novel by Alexandre Dumas, the title of which reminded him of the iron maiden torture device.
Therefore, the answer is a film adaptation of The Man in the Iron Mask from the novel by Alexandre Dumas , the title of which reminded him of the iron maiden torture device.