This song brought the Boo back after a long absence. The term "boo" (derived from the French "beau," meaning beautiful), caught on in the mid-'90s, and in 1996 the one-hit-wonder Ghost Town DJ's went to #31 US with a different song called "My Boo
." That same year, The Almighty RSO had a modest hit with "You Could Be My Boo," but that was the last of the charting Boo songs until this Usher/Alicia Keys collaboration.
The connection between the 1996 "My Boo" and the 2004 song is Jermaine Dupri: he released the former on his So So Def label, and he produced the later.