They state that there are many definitions out there about session beers, but they think the one provided on beeradvocate.com hits the mark.
Any beer that contains no higher than 5 percent ABV, featuring a balance between malt and hop characters (ingredients) and, typically, a clean finish—a combination of which creates a beer with high drinkability. The purpose of a session beer is to allow a beer drinker to have multiple beers, within a reasonable time period or session, without overwhelming the senses or reaching inappropriate levels of intoxication.
Anyways, get over there an read up on their suggestions for sessionable brews. My current favorite of this style is Easy Jack IPA from Firestone Walker with a close second going to Founder’s All Day IPA. Tell us about your go-to summer beers down below in the comments!