In Edgar Allan Poe's poem "The Raven", what is a Pallas or a bust?

I think that the line you are referring to from "The Raven" is the fifth line of stanza seven in which the narrator says, "Perched upon a bust of Pallas just above my chamber door..."

The narrator is telling the reader where the raven is in his study. The raven is sitting on a bust of Pallas. This would mean that the raven is sitting on a statue of the upper body (usually only the head and shoulders) of Athena, the Greek goddess of wisdom.