How is Plane (ODE) defined?

i’v read on this definition:

Create a plane geom of the given parameters, and return its ID. If space is nonzero, insert it into that space. The plane equation is
ax+by+c*z = d
The plane’s normal vector is (a,b,c), and it must have length 1. Planes are non-placeable geoms. This means that, unlike placeable geoms, planes do not have an assigned position and rotation. This means that the parameters (a,b,c,d) are always in global coordinates. In other words it is assumed that the plane is always part of the static environment and not tied to any movable object.

how did you implement the plane ? the input pins are a little confusing …