Exit weight divided by canopy area, in lbs/ft². Student canopies fly at 0.7–0.9, competition canopies above 3.0 — the same canopy gives a different number for a different body.
The number doesn't describe your canopy, it describes the relationship between you and it — and it decides how fast, how agile and how unforgiving that canopy flies. Higher loading mostly means one thing: less reaction time for mistakes. For jumpers under 500 jumps the USPA publishes a downsizing table setting how small the canopy may get. The expensive mistake is reading the number as a rank badge and downsizing on feel; coaches name 'I can fly that' as the sentence behind most bad downsizing decisions. The honest criterion isn't the number but what you can do reliably on your current canopy — flat turns, flare turns, crosswind and no-wind landings, landing on a spot. And design counts too: a cross-braced canopy at 1.5 is not the same thing as a semi-elliptical at 1.5.