Northern England When it's raining really hard and "Bucketing" down doesn't cut it. Also it sounds better.
Best used for the heaviest rain.
Stages of rain:
Spitting
Drizzle
Raining
Lashing
Pissing
Bucketing
BINNING
Person 1: Holy shit
Person 2: Sup?
Person 1: It's fucking binning it down outside.