Term coined by fandom for Dean's amulet, given to a teenage Dean by an 8-year-old Sam in 3.08 A Very Supernatural Christmas. It was very important to Dean, who wore it always until he discarded it in 5.16 Dark Side of the Moon.
First recorded use was after the events of 5.02 Good God, Y'All, in which Castiel took the amulet from Dean, because it will burn hot in God's presence. This led fans to speculate that the amulet symbolizes Sam's love for Dean, which would make the amulet "burn hot in God's presence."
After a disillusioned Dean discarded the amulet in 5.16 Dark Side of the Moon, fans immediately began speculating – and demanding – its return. However, the disposal of the amulet could be seen as symbolizing the start of Dean moving on from the old model of his relationship with Sam, which we see evolve in the latter part of season five.
A replica Samulet appears in the musical in 10.05 Fan Fiction. After Marie says Dean should never have thrown it away, he states he doesn't need it to remind him how he feels about Sam. However, at the end of the case, when she gives it to him, he keeps it and hangs it from the Impala's rearview mirror.