The Scone of Stone is the most famous form of dwarf bread. It has seated the Low Kings of the Dwarfs since it was first created to seat B'hrian Bloodaxe, some fifteen hundred years ago. The Low King cannot be Low King without it. The Dwarfs believe that the truth was once something solid, like the minerals they mine, and the last piece of it was hidden by Agi Hammerthief and baked into the Scone. Because the Scone contains a grain of truth it is said to burn red-hot if a lie is told in it's presence, a fact that came in useful when Low King Rhys wished to interrogate Dee and which prevents Ardent, the leader of the rebel Dwarfs from actually sitting on it when he steals the throne, knowing that he will be exposed. The Low King's use of the Scone like a lie detector to make Dee confess is very similar to how King Arthur used Excalibur to identify a traitor in the Camelot 3000 comic series, including the way the King knew, but did not mention, something about the detection-method's efficacy.
The Scone of Stone is a reference to the Stone of Scone (pronounced 'scoon'), or Stone of Destiny or Coronation Stone which is a block of sandstone on which the Scottish kings and later British rulers were crowned. Both it and its Round World counterpart were stolen by nationalists to return it to its rightful place in its country of origin. The name makes a natural parody for the dwarfs since a scone is a type of baked good and they make stone hard bread to use as food and as weapons. The Round World version was kept in the ruins of Scone Abbey in Scone, Scotland. The actual theft is referred to as a stupid crime because as Vimes points out, "other people would notice if you had a great rock up your jumper." In the Round World, the thieves did in fact get away without being caught but it was recovered and returned to Westminster Abbey before eventually being repatriated to Scotland in 1996 some 45 years later where it now sits in Edinburgh Castle. Rumours continue to abound that it was never really returned to Westminster and that the present stone is a fake. In Discworld the Scone is in fact a fake. Pratchett says that dwarf bread is more forged than baked because it is so rock hard. This is a play on words and foreshadowing because in The Fifth Elephant is clear that the Scone of Stone has been forged - ie is a forgery or fake since dwarf bread only lasts for a maximum of 300 years and belief has strange side effects. A copy of the stone is kept at the Museum of dwarf bread in Ankh-Morpork.
Another name the dwarfs give the Scone is the Low Throne, which is itself a parody of many a 'High Throne' such as that at Cair Paravel in the Narnia series by CS Lewis, Lloyd Alexander's Prydain Chronicles and in real life Brian Boru, The High King of Ireland who the Dwarf B'hrian Bloodaxe is based on. In Irish mythology, the lias fail (stone of destiny) is the traditional throne of the High King or Queen of All Ireland, and has a voice - it will scream or sing when the true High Monarch sits upon it. Later mythology is confused, but there is suggestion that it was stolen by raiding Scots, who in turn had it stolen from them by the raiding English...
The stone is also referred to as "the thing and the whole of the thing" which is a reference to Kantian philosophy's ding an sich' -- the "true" thing in and of itself, which is ultimately unknowable.
The Scone plays an important role in The Fifth Elephant.