Sometimes an "intro" is also used as a bridge. The intro to "They Can't Take That Away From Me," by George and Ira Gershwin, is used as a bridge later on, with different words.
[video=youtube;Fyq37gNjWuA]
BTW: Technically, the kind of intro the Beatles used with "If I Fell," and "Do You Want to Know a Secret" ("You'll never know how much I really love you. You'll never know how much I really care...") and was used with most of the songs written in the '20s, '30s, and '40s is referred to as "the verse."
Nat King Cole famously recorded a version of "Stardust" that featured only "the verse" (i.e., the intro), and not the main body of the song.
LCK