[Byron]

They are usually the result of many hundreds of crunches and leg raises in an exercise routine but many guys do start with a genetic advantage and with some body types they really struggle to get definition.
The defined abdominal area is considered very pleasing and desirable aesthetically - as any male model seeking work will tell you.

The abs are the muscles of the abdominal wall which can be made prominent with the appropriate exercises, just as a bodybuilder may want
to show big biceps for the arms.
They hold everything firmly in place (or not if they are neglected and so the pot belly) and are definitely not the intestines which, to put it in a very simplified way, are a long curling network of tubes for processing our food.