Well, that was easy, wasn't it.
Unfortunately the name of anything made of anything you can touch is also a concrete noun (even if you're unlikely to be in a position to touch it: like the sun, for instance, or Nicole Kidman).
The names of some things you can't touch that are concrete nouns, too: a rainbow, for example. Or a shadow.
Then there are things you can't touch or see, like a crash (the sort of crash you hear, I mean). Crash is a concrete noun, too.
So what sort of names aren't concrete nouns?
You're usually told you've got to think of something you can't detect with any of your senses, but unfortunately even that doesn't work, because although you can sense danger, for instance, danger doesn't count as a concrete noun - not even if it's approaching in the form of a large block of concrete that's about to drop on your head.
Danger is in fact an abstract noun (which is the other sort of noun).
I suppose you'd have to say that non-concrete nouns are those that have no physical existence, like kindness, or anger, or lacrosse...
,,,which just leaves us with the Problem of God, doesn't it?
Word To Think About Today: concrete. This word comes from the Latin concrētus, grown together or hardened, from crēscere, to grow.