"ABC-DEF-GHI" has appeared on at least 14 different Sesame Street-related albums since its debut, counting renditions by Big Bird and Elmo and appearances in medleys.
After finding the English alphabet written in chalk on the sidewalk, in one episode, Big Bird mistakes it for a very long word ("abcdefghijklmnopqrstuvwxyz"). With marching band-like accompaniment, he breaks into song, pronouncing the "word", as His brilliance as a bird, he thinks, will become known to all the world if he can ascertain the word's meaning.
A verse lists Big Bird's assumptions of what the word might mean:
It might be a kind of an elephant
Or a funny kind of kazoo
Or a strange, exotic turtle
That you'd never see in a zoo
It might be a kind of a doggy
Or particular shade of blue
Or maybe a pretty flower
Naah, not with a name like that, uh, uh!The bridge illustrates the daunting task of trying to spell, let alone pronounce the word:
It starts out like an A word, as anyone can see
But somewhere in the middle, it gets awful 'qr' to me.
In the Sesame Street TV series, Big Bird describes to Susan that he is "using signs to practice learning words" by "going up and down Sesame Street reading all the signs". After reading the signs "Sesame Street", "Stop", "Sale Yarn" and then says that there is a word he saw today, which he can hardly say and doesn't know what it means. He tells her it's ""), and she can't figure out what he's talking about until he shows her the alphabet printed in white letters on a green chalkboard. 
It is sung by Big Bird in Sesame Street.
The Alphabet song can also be sung in different sections and this way it is sung a lot faster. It breaks up a bit like this:abcdefghijklm nopqrstuvwxyz
as opposed to this:abcdefg hijklmnop qrs tuv wx yz