Well....it's not something that gets talked about by folks under the age of forty. I saw this come up today, and felt a duty to explain the term.
A dive-bar was typically a place which was very unglamorous....rarely sat more than forty people....usually did not have a TV or big-screen.....did have a 8-track or juke-box.....served about 90-percent cheap brands of beer, and mostly a hangout for guys.
You'd step into the bathroom and respect the fact that it was marginally cleaned once a month....typically out of toilet paper (unless you asked from the door)....and had barely heated in the winter months.
Dive-bars had at least three fights a year....mostly over things which were never remembered by the guilty parties involved.
Dive-bars were the typical choice of a place to hang out for vets from past wars.
Dive-bars rarely had a waitress on duty, and you ordered from the counter.
Dive-bars usually shut down by 11 PM....so working guys could get a few hours of sleep.
Dive-bars rarely served food....unless you were talking about salted peanuts.
Dive-bars are mostly extinct today....like the dinosaurs.