People online keep saying it's the best way to level after you reach 50+ but I can't find what it actually is. I assume it's some kind of advance quest, can anyone help me out and explain it?

SHAQ stands for super hard advanced quests VHAQ stands for very hard advanced quests.

@Lee-Ater to add to @Lwyu 's explanation, Very Hard Advanced Quest is preferred for experience, while Suoer Hard is preferred for finding rare weapons (with the added bonus of decent XP/H).

Super Hard for Advanced Quests require level 55, but some parties may want 70+. Very Hard can be done at level 40 and is by far much faster XP/H. (Experience per hour)

I'll do you one better, Why is Shaq and VHAQ? hehe, sorry... Avengers joke.

Shaq is a basketball player.

Vhaq is his parallel universe female form.

Also, they're different difficulty modes of Advanced Quests in Phantasy Star Online 2.