'Grade' refers to the ground- when you don't have a basement and lay the slab directly on prepared (compacted) ground. It could be at ground level or slightly above. If there is an attic space or a room below the slab then it's not a 'slab on grade'.
You were right in your assumption; though concrete slab on grade is a reinforced concrete slab and not PCC.
Thanks a lot!
Hm.. a reinforced slab on ground. So that would be like 'raft-foundation'?
Okay, I see.