There are certain gospels that seem to use an earlier document as source material. They share similar quotes and stories. The german reference for this document was originally reffered to as "Quella" or source. This became the "Q" document hypothosis.

"The Q document or Q (from the German Quelle, "source") is a postulated lost textual source for the Gospel of Matthew and Gospel of Luke. It is a theoretical collection of Jesus' sayings, written in Koine Greek. Although many scholars believe that "Q" was a real document, no actual document or fragment has been found." "The recognition of 19th-century New Testament scholars that Matthew and Luke share much material not found in their generally believed common source, the Gospel of Mark, has suggested a second common source, termed the Q document. This hypothetical lost text — also called the Q Gospel, the Sayings Gospel Q, the Secret of Q, the Synoptic Sayings Source, the Q Manuscript, and (in the 19th century) The Logia — seems most likely to have comprised a collection of Jesus' sayings. Recognizing such a Q document is one of two key elements in the "two-source hypothesis" alongside the priority of Mark. (See also the Gospel of the Hebrews and Streeter) The two-source hypothesis is the most widely accepted solution to the Synoptic Problem, which concerns the literary relationships between and among the first three canonical gospels (the Gospels of Mark, Matthew, and Luke), known as the Synoptic Gospels. Similarity in word choices and event placement shows an interrelationship. The synoptic problem concerns how this interrelation came to pass, as well as the nature of this interrelationship. According to the two-source hypothesis, Matthew and Luke both used the Gospel of Mark, independently of one another. This necessitates the existence of a hypothetical third source in order to explain the double tradition material where there is agreement between Matthew and Luke that is not in Mark. This hypothetical source is named Q out of convenience." "If the two-source hypothesis is correct, then the second source, Q, would almost certainly have to be a written document. If Q were merely a shared oral tradition, it could not account for the nearly identical word-for-word similarities between Matthew and Luke when quoting Q material. Similarly, it is possible to deduce that the Q document, in the form that Matthew and Luke had access to, was written in Greek. If Matthew and Luke were referring to a document that had been written in some other language (for example Aramaic), it is highly unlikely that two independent translations would have exactly the same wording. The Q document must have been composed prior to the Gospels of both Matthew and Luke. Some scholars even suggest Q may have predated Mark. The Q document, if it did exist, has since been lost, but scholars believe it can be partially reconstructed by examining elements common to Matthew and Luke (but absent from Mark). This reconstructed Q is notable in that it generally does not describe the events of the life of Jesus: Q does not mention Jesus' birth, his selection of the 12 disciples, his crucifixion, or the resurrection. Instead, it appears to be a collection of Jesus' sayings and teachings." Source and further information: http://en.wikipedia.org/wiki/Q_Document

It's like the X Files.

The "Q" Document(Q short for quelle, or source in German) is believed to be the basic document from which the Gospels of Matthew, Mark and Luke originated. Two other apocryphal Gospels, Sayings of Jesus and Gospel of Thomas may have come from the same source. No complete copy of the Quelle document has yet been found but fragments exist. +3