PlayStation Plus Essential is a tier of PlayStation Plus that includes a small collection of monthly games (usually two or three) that can be played at no additional cost (i.e., they are "free" once you have subscribed to this service), as well as a few other benefits online multiplayer and cloud saves. The included games change monthly and are listed below. There are three tiers of PlayStation Plus in total, with the "Essential" tier being the lowest one.

PlayStation Plus Essential: Monthly games, online multiplayer, and cloud saves
PlayStation Plus Extra: Large included game catalog
PlayStation Plus Premium: Classics and streaming games in game catalog

PlayStation Plus Essential can be joined either via the official PlayStation web site, or by purchasing a PlayStation Plus gift card from a retailer like Amazon or Playasia.