A plot-bunny (idea for a story), especially one related to The Lord of the Rings. Originated at OFUM. It takes the form of a 'bunny' because of its resemblance to the Norwegian word for 'soft'.
"Nuzgul" originated as a mini-Balrog misspelling of "Nazgul," the undead Ring-wraiths from Tolkien's Middle-earth, but soon developed its own meaning.
"I just got a nuzgul that wants me to write about Rosie Cotton's childhood."