Apocalypse World is a narrative-focused tabletop RPG by Lumpley Games with an open post-apocalyptic setting. Use this tag when your question concerns the second edition of the game, released in 2016 through Kickstarter and 2017 for general sale.
Apocalypse World is a role-playing and storytelling game set in a vaguely defined post-apocalyptic world. The original version of Apocalypse World gathered a strong following and spawned several hacks using the game's engine, called Powered by the Apocalypse. The second edition of Apocalypse World was funded with a successful Kickstarter campaign in 2016 and released for sale in 2017.
The gameplay revolves around the simple principle of "to do it, do it" - meaning that a player has to narrate their character's actions to trigger more mechanical rules called moves. A move may result in the player rolling 2d6 to determine whether the outcome of the action is a success, partial success or a failure, with the possible effects of each outcome being usually known in advance. The GM is urged to avoid pre-planning the stories to leave room for emergent stories caused by the luck of the dice and player freedom.
Another significant feature of Apocalypse World is the heavy emphasis on character classes, usually referred to as "playbooks" as each one comes on its own, customized character sheet. Playbooks have a variety of unique mechanics that dramatically reinforce a character's identity: a Hardholder runs an armed stronghold, a Battlebabe packs customizable weapons, a Savvyhead can build anything in their garage, etc. As characters advance in experience, they can take custom moves from other playbooks, resulting in more nuanced characters.
The second edition of the game changes little about the core mechanic, but introduces a wide variety of new moves, threat types, playbooks and character options, some of them adapted from the extended playbooks of the first edition.
Use this tag when the question specifically concerns Apocalypse World 2e content, or when the question should be answered based on 2e content specifically.