OK so we have two different names for some lugs, so let's start by finding out what exactly they are.
Where are you going to find these lugs? Well, inside of a panel board of course! Now, if you’re not familiar with the term panelboard, check out episode 35 here where I talk about the difference between a panelboard and a load center.
First of all, one of the biggest differences between a sub feed lug and a feed through lug is the location inside the panel. One is on the top with the main and the other one is on the bottom.