This is a lightly moderated board for several reasons.
As Laika said, it's a handful of volunteers who do it and they aren't always online.
Also, it isn't like Reddit where you have dozens of people who will downvote and report stuff, the mods are mostly on their own and they participate in the discussions themselves. If they come across something while they are participating they might take action but they aren't going back and scouring threads for potential offensive posts.
Finally, this board/community has been around forever and the mods have a good pulse on how heavy they should moderate and the people here seem to prefer that it operates like the internet of 8-10 years ago where people simply ignored what they didn't like rather than the mods having to take action.
So all told, as far as how heavily this place is moderated I'd say that it isn't 4chan around here, but it also isn't Reddit. It's probably somewhere around what Twitter is like now.