The Definition
What’s a gastropub? Interestingly it’s one of those words that didn’t mean much of anything just over 15 years ago, but has since been made up and seemingly adopted and by enough people it’s now accepted (at least in most communities.) According to the Red Drum Gastropub here in the Lowcountry, the word Gastropub is identified as follows:

Gastropub (n): A new type of eating place bridging the gap between booze
joints and upscale restaurants. These cuisine-conscious taverns started to
appear about 15 years ago in England. Gastropubs have become the London
equivalent of the French brasserie, with good food that’s also a good
value.

And answers.com describes the term as:

A gastropub is a British term for a public house (”pub”) which specializes in
high-quality food a step above the more basic “pub grub.” The name is a
portmanteau of pub and gastronomy and was coined in 1991 when David Eyre and
Mike Belben opened a pub called The Eagle in Clerkenwell, London. They
placed an emphasis on the quality of food served, though The Eagle was not
the first pub to offer good food.

Gastropubs usually have an atmosphere which is relaxed and a focus on offering a
particular cuisine prepared as well as it is in the best restaurants. Staying
true to the format requires a menu that complements the assortment of beers and
wines the gastropub offers.

Some describe gastropubs as the
Anglo-equivalent of the French brasserie or the
Japanese izakaya.