The Dead Sea Scrolls (裏死海文書) is the in-universe name for the Secret Dead Sea Scrolls, a set of documents that serve as the primary guide and philosophy of SEELE. Little is known about the Dead Sea Scrolls from the series, except for what SEELE alludes to during their meetings and what is stated in the Classified Information section of the Neon Genesis Evangelion 2 video game.
It is known that the Scrolls are of extraterrestrial origin and that they serve as a manual on the use and purposes of the contents of Black and White Moons; a Seed of Life and the Spear of Longinus. They detail rules on how to use these items, and are often referred to as a prophecy of sorts; right down to the extent of the order and times of release or arrival of the Angels.
SEELE possessed vast wealth and power, and being founded originally as a religious organisation they funded investigations into relics of their faith. This culminated with the excavation of the Secret Dead Sea Scrolls. Upon discovery they were taken to their headquarters. The irrelevant discoveries were released to the public as the Dead Sea Scrolls, while the Secret Dead Sea Scrolls were kept by SEELE. They would later be used to put their ultimate plans of a Second and Third Impact, followed by Instrumentality into fruition.
According to Gendo, the Dead Sea Scrolls do not tell everything.
In Rebuild of Evangelion
In the three first films of the rebuild series, the Dead Sea Scrolls are a similar role to those in Neon Genesis Evangelion.
The first scroll shows several angels (the 4th, 5th, 7th and 10th), 4 similar winged beings (probably the Adams), a 4-armed being (probably Evangelion 13), a tree and a being holding a spear and a writing resembling Sumerian.
The second scroll shows an elder being emerging from a space surrounded by people and two gigantic legs
In Real Life
The real Dead Sea Scrolls were discovered in eleven caves at Qumran in 1947 on the northwestern shore of the Dead Sea. The texts are mostly fragmented, with the exception of a few relatively intact scripts. Scripts and script fragments are numbered according to the cave they were found in. A number of scrolls are in Hebrew, while others are in Aramaic. Fragments of every book of the Old Testament, except for the book of Esther, have been found among the Dead Sea Scrolls.
A number of Dead Sea Scrolls had not been made available to the public at the time of the series' production which have since been released, and the mystery surrounding their contents has disappeared.