From Muppet Wiki

Written by
Music by	Alan Menken
Lyrics by	Luis Santeiro
Date
Source
Publisher	Sesame Street Inc.

"What is Friend?" is a Sesame Street song sung by Cookie Monster in the early 1990s.

At the beginning of the segment, Cookie Monster announces that it is snack time for him and a friend, but there ends up being only one cookie left. Cookie Monster then sings about friendship, wondering what to do about the situation, and by the end, Cookie Monster gives his friend the cookie. Although the friend suggests sharing the cookie, Cookie Monster opts to eat the brick wall they were standing behind.

In 2000, this song was remade on the Street set with Lulu and Cookie Monster. While the song had the same melody, this new version was slightly slower than the original version, and rather than devour something else, when Cookie Monster gives his last cookie up, he remarks, "Me feel strangely okay about this." (EKA: Episode 3885)

The 2000 version was also featured over footage of real kids being friends. (EKA: Episode 3916) This version was partially used in the timeline sequence of The Street We Live On.