"It's just an open E with an A flat (G#) octave played at the 11th fret, but what's funny about it is we've now used it in so many songs that when other bands use it, even if they're not trying to emulate us, people always tell me, 'Oh, they sound like Smashing Pumpkins.' I like the idea of having exclusive claim to one chord." - Billy Corgan
Many guitarists will be familiar with the "pumpkin chord". While it (obviously) wasn't invented by Billy Corgan - Jimi Hendrix is notable in his use of it; but he already has his own chord(s) - the Pumpkin's have used it in so many of their songs over the years (Rhinoceros, Cherub Rock, and Drown come to mind) that it's become synonymous with their sound.
While THE pumpkin chord, as Billy describes is, is played with an open E and a G# on the next octave:
e|----|
B|----|
G|----|
D|----|
A|-11-|
E|--0-|
...any 'chord' that consists of an open E and a note somewhere up the A string is often referred to as a pumpkin chord. | 
