idspispopd.
Sure, it's handy for walking through walls while battling demons in
DOOM, but what does it mean?
Well, according to the doom source code: (Available from idsoftware.com's FTP)
st_stuff.c line 53:
// Smashing Pumpkins Into Samml Piles Of Putried Debris.
And the prefix "id" is shared by all the cheats, being that
ID created
DOOM.