The first solid poo to make an appearance after a long hard fought with diarrhea, signalling that the tide has turned.
In 'The Lord of the Rings: The Two Towers', the Battle of Helms Deep is all but lost until Gandalf the White appears, handing victory to the men of Rohan against the Uruks of Isengard.
Similarly, the arrival of Gandalf the Brown reveals that the battle for control of your bowels has been concluded in your favour.
Guy 1: You coming swimming later?
Guy 2: I can't, I have a bad stomach, I need to rest.
Little known slang term for toilet paperusually of the softer variety. Comes from the fact that Gandalf from Lord of the Rings has a long white fluffy beard.
Gandalf the green is a term used for a marijuana dealer that messages you notifying you that he has just got weed if you are looking for it when all other dealers have failed you.