Biblical: The first human, created from sand by God following the creation of animals.
Evangelion: The hybernating angel that lay dormant in Antarctica. In pursueing the human instrumentality project, Seele sent a team to go dig Adam out of the ice. Something triggered him to self-destruct, and the ice cap melted. There was a monumental flood, and it led to the extinction of half the world's population. The incident was called the Second Impact (the first being the meteor that hit the earth and led the dinosaurs to extinction). It was covered up, saying that a meteor struck the ice cap (hence the cover-up name). Adam was again found, in a fetal state, and was then encased. He was later embedded into Gendou Ikari's hand in order to make Third Impact possible.
All of the Angels are hunting for Adam, but mistakenly take their search to Lilith, believing she is him. The first Angel to realize this folly was Tabris.