Wikipedia
Metroidvania is a subgenre of the action-adventure video game with gameplay concepts similar to the Metroid series and the Castlevania series (specifically from Castlevania: Symphony of the Night and onward). The genre name is a portmanteau of the two series' names. Other names include Castletroid, a similar portmanteau; Igavania, in reference to Koji Igarashi, a major developer of Symphony of the Night and many other Castlevania games and whose contributions have shaped the design of the subgenre; Metroid-style games, Metroid-like games, and other, similar formations invoking similarity to Metroid.
Metroidvania games generally feature a large interconnected world map the player can explore, though access to parts of the world is often limited by doors or other portals that can only be opened after the player has acquired special items, tools, weapons or abilities within the game. Acquiring such improvements can also aid the player in defeating more difficult enemies and locating shortcuts and secret areas, and often includes retracing one's steps across the map. Through this, Metroidvania games include tighter integration of story and level design, careful design of levels and character controls to encourage exploration and experimentation, and a means for the player to become more invested in their player character. Metroidvania games typically are two-dimensional platformers, but can also include other genre types. Though popularized during the early console generations, the genre has seen a resurgence since the 2000s due to critically praised, independently developed games.