I would think that a "basic quad" would be one where four people are involved in a relationship with one another in some form. However, we all know that poly doesn't follow rules, and I've heard of all different kinds of quads.
In my quad the men are intimately involved with both women but not each other. The women are intimately involved with both men and each other. I don't identify as bisexual but consider Asha my girlfriend and am physically attracted to her, so go figure.