Wing loading is the amount of weight that a wing is required to support aerodynamically. This is normally expressed (in the U.S. at least) as a ratio of pounds per square foot. For instance 1.3:1 would mean 1.3 pounds of weight is being supported by 1 foot of wing area. You'd speak that ratio as 1 point 3 to 1.
To arrive at these numbers, take the entire weight the wing needs to support, in our case we can use exit weight, and divide that by the area of the wing. A typical example might be a skydiver with an exit weight of 235 pounds. That weight includes EVERYTHING; skydiver, goggles, gloves, lead, rig and even the canopy itself.
If, for instance, that skydiver was planing on deploying a Spectre 190, then he'd have a wingloading of about 1.238:1.
This wingloading number is really only relevant to that particular model and size of canopy and would not give the same performace as a, for instance, Sabre 190. The two canopies would fly COMPLETELY differently even under the same wingloading.
Further, if the skydiver decided to downsize to a Spectre 170, he'd have a wingloading of about 1.382:1 and that canopy would also perform differently than if he'd increased his exit weight on his Spectre 190 to 262.65 pounds to give it the same wingloading.
Wingloading doesn't scale for performance issues.
Wingloading is only ONE factor in performance, however, generally speaking, lighter wingloadings can give softer and slower landings than higher wingloadings on the same model and size canopy.
Canopies are designed with a wingloading range in mind and moving to either extreme of too light or too heavy will degrade performance.
Nice explanation Paul. Did that make sense Nelson? As paul stated, it's only one method to determine how a parachute "ought" to act over your head. Different parachutes perform differently at the same wingload in most instances, but not so much that you cant use the number as a good benchmark.