idspispopd

The walk through walls cheat mode for Doom.

Simplified in DoomII to IDCLIP.

IDKFA
IDDQD

You could cheat in Network games by typing IDDT (reveal map) three times.. see them sneaking... launch a rocket to greet your friend as they opened the door.

hehe..

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.