Guild Wars 2

I keep hearing this and have not found a definition for it on google, can someone please enlighten me as to what it means?

It’s a build that focuses solely on survival. This is most applied to spvp instances. One question i wanna ask is are bunker builds in spvp effective in pve as well?

A "Bunker" build is a build designed to do exactly what the name suggest, and be a bunker. Allies take shelter near you, as you, with your amazing defensive skills, can easily defend them.

To answer your question, penatbater, they are hugely effective in PvE as well. However, they are uncommon, for a variety of reasons:
1: Almost everyone likes to do big damage.
2: Almost everyone thinks Greatswords look coolest.
3: Everyone has their own survivability mechanics, and if they use them properly, will never need you.