What is PxHullPolygon::mPlane[] exactly?

The reference says:

PxReal PxHullPolygon::mPlane[4]

Plane equation for this polygon.

What is the equation though, in terms of the 4 numbers stored in mPlane?
Specifically, what is the best way to interpret this information for openGL drawing?

Planes are typically written in the form:

Ax + By + Cz + D = 0

Where A,B,C,D are the 4 values in mPlane.

This can be seen as a plane with normal (A,B,C) with a signed distance D (assuming normal is unit length) from the origin.

Hope that helps.

That helps, thank you.
I do have a followup question about rendering, but I think it will be best to start a new thread for that.