What is "whoopie pie"

n. A baked good consisting of two round, mound-shaped pieces of cake (typically chocolate cake) with a sweet, creamy filling or frosting sandwiched in between.

The whoopie pie (alternatively called a black moon, gob [term indigenous to the Pittsburgh region], black-and-white, bob, or "BFO" for Big Fat Oreo [also recorded as "Devil Dogs" and "Twins" in 1835]) is a US baked product that may be considered either a cookie, pie or cake. It is made of two round mound-shaped pieces of chocolate cake, or sometimes pumpkin or gingerbread cake, with a sweet, creamy filling or frosting sandwiched between them.