Wubba is the cornerstone of Sesame Street monster language. Though used frequently throughout the show's history, its exact translation in monster is unknown. Former head writer Norman Stiles states, "It's what monsters say." It is known, however, that repeating the word while hopping up and down does not activate a computer or open a closed phone booth.
The earliest known usage of the word can be traced to the 1972 song "Imagination," where a frightened Ernie cites it as a scary thing the monsters in his head say. The experience had a lasting effect, as he would later use the bellow on Bert in a sketch where he tries to scare his roommate.
Since then, the word has been used for various monster activities, including the "Wubba Wubba Boing Boing" game in Episode 3663, as the repeated chorus of Grover's music video "Monster in the Mirror", and a chant used when monsters get together as described in a book read by Laura Bush in Episode 4032.
In fact, the name can be accredited to a type of monster, cited by Kermit the Frog serving as a Smart Person doling out advice to Mr. Ferbilfeemer for how to avoid such a creature. The Great Grey-Green Greasy Wubba Wubba Monster is described as a beast who slithers across the floor with big claw-like feet, pokes its prey in the ribs, and goes "gackle-gackle!" This creature is so fearsome, that it haunts Mr. Snuffleupagus, terrorizing him with horrible nightmares in Episode 0832.
The word transcends the New York City radius of monsters and is heard in England at The Furchester Hotel, where Phoebe Furchester-Fuzz includes the word in her catchphrase ("Fuzza-wubba!"). It is also a favourite word of Phoebe's great-grandmother who, during her own time running the hotel, used to "welcome" guests by jumping up from under the reception desk and shouting it at them (Episode 233: Great Grandma). The word has since proven to be popular not just with monsters, but with cheeses as well, as one particular slice appearing in episode 4523 claims to enjoy saying the word.