Wikipedia uses the abbreviation MOBA for League of Legends’ genre.
MOBA stands for “multiplayer online battle arena.” In League of Legends, two teams of players control individual champions on a structured battlefield, usually trying to destroy the opposing team’s main base. Each champion has distinctive abilities, and players strengthen their characters during a match through experience, gold, items, and objectives.
League grew out of the custom-map tradition associated with Warcraft III, especially Defense of the Ancients. That lineage is why some older sources use labels such as “action real-time strategy” or “ARTS,” while others describe the game more broadly as a strategy or action title. Wikipedia’s infobox uses MOBA, making it the canonical answer for this wording. League is not an FPS, because its core combat is not played from a first-person shooting perspective; it is not an MMORPG, because matches are discrete competitive sessions rather than one persistent online world; and RTS usually implies controlling armies or building bases, which League does not.