It is anything but a Full-Fat IPA, nor is it a Pale Ale, nor a British-styled sessionable pale beer, rather it fills in a hoppy Venn outline of those three beer types. Lessen the strength in an IPA, lose a portion of the maltier middles of a Pale Ale, load up the hops on a golden ale, dry it hard and fast and give it a pokier bitterness and you're in the Session IPA zone. Given their pace of growth and their now-omnipresent presence in bars and bottles shops, we're all in the Session IPA zone.
The name Session IPA references the 'meeting', that fine British method of drinking many lower-alcohol beers over an all-encompassing timeframe. It is anything but a cognizant let's-have-a-meeting sort of thing, it's all the more simply the long-standing social way to deal with drinking. We appreciate a meeting of drinking. The beers are sessionable. They're meeting strength. A major American IPA isn't sessionable in the six-pints-today sort of way that Brits appreciate mingling, and that roused the name.
Meeting IPA is apparently an American innovation. I state apparently in light of the fact that I figure Brit brewers really designed Session IPA or the soonest form of it, however they simply didn't want to hyperbolize it with a cool new name. Those British breweries consolidated components of exemplary English ales, they made them lighter and more splendid and included heaps of citrusy American hops late into the brewing cycle to expand their aroma, making 4% pale beers with a major American trademark.