Click the structures and reaction arrows in sequence to view the 3D models and animations respectively
E1 describes an elimination reaction in which the rate-determining step is unimolecular and does not involve the base. The leaving group leaves in this step, and a proton is removed in a second step. This is an example of an E1 reaction which shows the formation of an alkene.
J. F. Bunnett, Angew. Chemie Int. Ed. English, 1962, 1, 225–235.