The Ordial Plane is not canon
While it's a cool idea, the concept originated, as far back as I have found, on mimir.net, and became a popular fan idea from there. But as I say, it was a reasonably well-designed idea and there was a niche the author wanted to fill, so let's talk about that.
The Ordial Plane is the Plane of Proof
The cosmological model of 2nd Edition supposed that the Inner Planes were connected to the Prime Material Plane via the Ethereal, while the Astral connected the Prime to the Outer Planes. What, then, connected the Outer (where many gods reside and receive belief) to the Inner (which are solid and constituted of elemental matter, and where elemental magic does function)? Between belief and substance, the posit was, lay Proof.
The theory suggested, originally, that this was the cosmological role of the Ordial Plane: an unknown plane which provided conduits for belief to reach gods in the Inner Planes, and for the thoughtscapes of the Outer Planes to be made real and tangible. It also proposed that deities with unknown realms might be hidden on the Ordial, where they would have access to belief and substance without being easily located by planar travelers.
Of course, such idea seeds tend to germinate, and this one bore a great deal of fruit. Later fan work has suggested many different possibilities for the nature and the role of the Ordial Plane: that it is where the true essence of deities resides; that vestiges are bound to this plane; that it is what Primes know as the "Spirit World" and the source of animist powers or even the souls of Prime beings. Later publications have contested that one - Bastion of Broken Souls tells us that souls arise in preincarnate form from the Positive Energy Plane (although you could certainly work the two together easily enough).