MMA is a Mixed martial art, it means you can use all skills (Karate, Judo, BJJ .. etc) so even if the fight goes on ground the referee won’t stop the fight. So MMA is not a standalone martial art by it self, but it’s the acceptance of all martial arts to be performed together in a single fight. BJJ is a single type of martial art, it focuses on chokes and breaking joints, no striking or kicks are allowed. Muaythai is a single type of martial art, it’s a pure striking game with kicks, game will stop once fighter falls on ground.