I need this thread stickied in case someone brings up a word I don't know.

What does "Arc" mean exactly?
I basically understand it contextually but have never known the exact definition.

It's a smaller story that is apart of the whole story.

In anime there is often one big plot and smaller plots or story within the whole series, which is an arc.

Sorta like a sub-story which is a segment of the larger story. Not all series have it though. For example:

SAO has two arcs so far: Sword Art Online arc and the ALfheim arc
Kuroko no Basuke: Qualifiers arc, Inter-High arc, Winter Cup arc

There's no general set "length" for an arc, some arcs can last one episode, some can last fifty. Like Naruto's. But they're generally continuous. For example, big sub-plots of Sakurasou are Nanami's voice auditions or Sorata's game design, but they're not arcs since they last pretty much the whole series and make up the plot.

Arc: To me, a story that connects to the main plot. It can be long or short.

Why is there a whole section dedicated to this?

Can't be because entire series focusing on that point?

That's pretty messed up.

There's hardly any that go full on incest, 99% of the time it's step brother/sister by marriage.

Infact, the only one that I know that goes the full incest route, is Oreimo (Which is a fantastic series).

As much as intense tsundere annoys me, I enjoyed Oreimo quite a bit.

I found an example for some of the terms
brocon/siscon:
Yaoi,loli (also counts as trap)
Trap: