Questions about the 'Q Source', a hypothetical collection of some sayings of Jesus that is assumed to be the source material for the overlapping parts of Matthew and Luke not found in Mark.
Q (short for Quelle, which is German for "source"), is part of several proposed solutions to the synoptic-problem. It is also sometimes referred to as the Q document or Q Gospel.
Q represents a hypothetical collection of some sayings of Jesus that is assumed to be the source material for the overlapping parts of Matthew and Luke not found in Mark. On some theories of Markan Priority, Matthew & Luke each independently drew material from Mark and drew material from Q.
Advocates of Q generally hold that neither Matthew knew Luke's Gospel nor did Luke know Matthew's.
No manuscript or patristic testimony has been found for Q. During the 19th century there were scholars who suggested that the "logia" mentioned by Papias may be this common source; scholarship has largely abandoned that view today.
For more information pertaining to why scholars propose this hypothetical document, see "What is the evidence for the existence of the Q document?"