What are proc coefficients?

all skill have a proc coeficent ranging from 0 - 1. Used to determine how often certain bonuses trigger.
EX1
Let's use LOH as an example. Its a skill that gives you health for every enemy hit. It is usually comes from items. But LOH is a proc skill. this means that it only activates [proc coefficiaent *100]% of the time. so if you have 1000 LOH and you are using a skill with a proc coeffiencet of .5, then against a single enemy, you can expect back an average of 500Life/hit. There are alos coeffiencts to deal with the second and more enemies hit.
blizz takes into account the speed of the skill and the AOE when determining prosc. Just to be clear. These are not dynamic numbers. Thye only change view updates and hotfixes.