The travel time and distance a person is willing to endure in order to obtain and / or smoke weed. The term can be used for any amount of weed, from a large supply to simply enough for one night.
It is important to note that the term does not strictly refer to time or distance, but can be applied to either.
Wayne: "Man, I spent an hour on the bus and then another half hour on the train the other night just to get to a mates house and smoke some weed."
Darrel: "Dude, you got some long weed range."