A concrete noun is a noun which can be identified through one of the five senses (taste, touch, sight, hearing, smell).
Would someone please answer the phone?
Phone is a concrete noun: I can touch it, see it, hear it, and maybe even smell it or taste it.
What is that noise?
Even though noise can’t be touched – and the noise may even be coming from several places – I can hear the noise, so it’s a concrete noun.
After his retirement, Mr. Bond pursued his dream of photographing rainbows.
Rainbows is a concrete noun: it can be seen. Mr. Bond is also a concrete noun, but dream and retirement are not. (See Abstract Nouns.)