"Ouroboros" is the name for the circular symbol depicting a snake or dragon swallowing its own tail - a sign for wholeness and infinity.
Rowena and Sam present to Dean, Jack, and Castiel that they believe they are hunting a Gorgon. Before Rowena says what they think they're hunting, Dean says, "This is like an A.V. club presentation." This is a nod to the show Stranger Things, Which follows a group of A.V. Club kids that are fighting a Demogorgon in the first season.
Last of seven episodes of Katherine Evans as Maggie.