International Pokemon League
Pokemon Trainers have various ranks (both official and unofficial) to denote the general power level of any given trainer.
The Generic name for everyone that competitively battles Pokemon. Amongst the ranks of the Pokemon Trainer, the amount of badges a Trainer has generally (but not always) denotes their power level.
Master Pokemon Trainer “Pokemon Master”
Master Pokemon Trainers, or Pokemon Masters in the vernacular, is usually a person who has defeated an entire League’s worth of Gyms and Elite Pokemon Masters. However, it is also generally used as a power level. so even people that have not defeated a single Gym but are extremely powerful may be referred to as Pokwmon
A Gym Leader is a Pokemon Master, generally devoted to a specific type of Pokemon, that has settled down to train Pokemon Trainers. They are required to have Pokemon available for beginners to train with, to get used to Pokemon Training. These Pokemon are also usually the Pokemon they fight Pokemon Trainers that challenge the Leader for their Badge.
Elite Pokemon Master
Often just called Elites, Elite Pokemon Masters are a highly select group of trainers that have defeated an entire League’s worth of Gym Leaders and Elites when said Masters were using their actual belt team. The last Elite that they defeat is the Elite that they replace.
League Champion Pokemon Master
A League Champion is hands down the most powerful Pokemon Master in a given League. Any Master, at any one time, can only hold the position of League Champion Pokemon Master in a single League.