We're not bitter. Really, we're not. Bitter is a British term for pale ale. Boy's bitter is less than 3%ABV, while a strong bitter has at least 7%ABV.

By 1830 the terms bitter and pale ale were synonymous. Breweries would tend to designate beers as pale ale, while customers in pubs would commonly order bitters. Same thing.

Today, one could say that in Britain, if a pale ale is in a bottle, it's pale ale. If it's on tap, the same beer is a bitter. Here's your roadmap:

Session or Ordinary Bitter: up to 4.1% Regular or Best Bitter: 4.2% to 4.7%
Premium or Strong Bitter: 4.8% and above. Also known as Extra Special Bitter, or in the USA, ESB.

VS ESB: You heard it here first. We've never run across this term before, but we thought it suited a strong bitter. Very Special Extra Special Bitter.

ESB is used in the USA because craft brewers are afraid of calling their beer bitter--that's before IPAs became all the rage. That's certainly true in our case. In 1992, we considered calling Barley's Pale Ale, Barley's Bitter, because that's what it is (see above.) We didn't because (see above.)