that'd be soil, in my head, anything that has a bunch of humus, and composted organic material is soil.
but why does that make a difference?
If it were me i'd add more aeration and peat to that mix.
or aeration and coco.
also depends on what type of compost you have.
Thanks for the responses. Yeah, I guess I'll go with "soil". Worm castings can be considered a biological component of soil. There are worms in soil, right? Compost is organic matter, full of organisms and even though it may be only 5% of soil makeup, we all know its benefits. I have plenty of both in this pro mix. : )