Biff is Buford's goldfish which gets lost at the beach in the episode "Voyage to the Bottom of Buford". Buford has stated that he named his fish after his mother.
Getting Biff at a carnival was an important event in Buford's life. When a bully tried to eat Biff, Buford became a bully himself in order to get Biff back. During Voyage to the Bottom of Buford while Biff was lost, Buford became extremely emotional and sensitive, revealing how much he cares for Biff. He then saves Biff again, this time from being eaten by a giant squid, and apparently loses the fear of squids after saving him.