It depends on the rule book you are using. There are six editions of shadowrun :) I currently only have access to SR4 and SR5.
Edge in all of them is 'luck'. The idea that the PCs can influence the die and be more heroic.
- SR4 There aren't priorities I think, so I'm guessing it's not this
- SR5 You can add to 'special attributes' depending on your race.
With SR5 if you pick human as priority A you have 9 points you can spend on 'special attributes'. With priority D only three points. Those special attributes are either Resonance (for technomancer) magic (for ... well ..magic users) or edge.
You start with a value of 1 in edge. So if you don't spend anything you still have 1 pt.
So if you are a mundane person the value you will have is 1 (the starting value) plus the value in the priority table. BUT the cap is 6 still (baring the spending of qualities). So don't pick a priority with >5 or you just wasted your points.
If it's a different edition, just ignore the above!