What Genre is Dark Souls III?

Dark Souls III is an online game that follows a single player through a set storyline, but because it is also online I can't decide if it's an MMORPG or something else.

Solution 1:

Dark soul is NOT a MMORPG, it is simply a fantasy rpg action game that can also be played online.

This quote from wikipedia will help you understand what a MMORPG actually is:

MMORPGs are distinguished from single-player or small multi-player online RPGs by the number of players able to interact together, and by the game's persistent world (usually hosted by the game's publisher), which continues to exist and evolve while the player is offline and away from the game.