An enormous, yellowish-tinged patch of moisture that appears on a surface that has been lived-on by a large, smelly creature for a long period of time. The most common place for this to appear is on the bed of the being in question, or possible the rim of a toilet seat. The moisture usually consists of a build up of smelly odours given off by the creature.
'Bloody hell, did you see that danpatch on Mills' bed? He seriously needs to stop sweating so much.'
'You think that's bad, you should see the colour of his toilet seat'.