This is correct, it came from EQ where proc became a common term and it basically mean anything with a chance to happen on hit. As a paladin the mains ones are Seal of Righteousness, Seal of Command, Seal of Light, and Seal of Judgement. They don't apply the actual effects with every hit but they have a chance to do so on every hit. World of Warcraft has taken this a little bit further and limited the number of times per minute on average a "proc" will occur so that slow weapons proc alot more often than fast weapons since you don't get as many swings with them in a minute.