A large penis.
The term comes from a Lenny Bruce routine about African-American men ("Their wangs look like a
baby's arm with an apple in its fist" as immortalized in his
book _How to Talk Dirty and Influence People_), but this exact wording is taken from The Tubes' song "What Do You Want From
Life", from their first album.
Since not everyone gets the reference, the term typically is used as an in-joke.