The Q document, named from the German word "Quelle", which means "source", is a hypothetical lost textual source for the Gospel of Matthew and the Gospel of Luke. Biblical scholars have long realized that that Matthew and Luke share much material not found in the Gospel of Mark, and postulated a second common source, which was named the Q document, containing the sayings of Jesus but no account of his early life. Some non-canonical writings, such as the Gospel of Thomas, also are believed to draw from Q.
Nevertheless, it should be borne in mind that the Q document is only a hypothesis; there are no surviving manuscripts nor is a Q document referred to in the Bible. It is entirely possible that the same elements could be accounted for via oral traditions, some variety of since-lost texts, or if the Gospels of Matthew or Luke used the other as a source. Some religious historians believe that Q can be reconstructed by analyzing those passages Matthew and Luke have in common.