The title of this article is a conjectural. Though the topic is found within The Simpsons universe, a proper name is not available.
“Hey remember that pet gerbil we use have... He didn't run away after all”
―Bart after looking under the couch
The Simpson family's unnamed pet gerbil was owned by the Simpsons, originally they believed that it ran away when it went missing until when they were looking for the missing puzzle piece. Bart looked between the couch and finds that the gerbil didn't run away, instead it was crushed by someone sitting on the couch.