Pokémon manga (Japanese: マンガ), unlike the Pokémon anime, does not actually refer to one specific manga or one particular piece of Pokémon canon but, rather, an entire subcategory of comics written with their own storylines and interpretations of the Pokémon world. These frequently have no connection to one another beyond their medium.
Many Pokémon manga are never translated into English. This is likely because of manga being more traditional in Japan. Additionally, some series contain scenarios and artwork considered inappropriate for Western audiences. Sometimes the artwork is cleaned-up for foreign publishing, as was the case with The Electric Tale of Pikachu manga, but some Japanese publishers prefer not to have the artwork changed.
That's the definition of the Pokemon Manga from Bulbapedia.
Manga have 7 different types: Main Game Adaptions, Spin-off Game Adaptions, Anime Adaptations, Movie Manga Adaptations, Original Stories, Pokemon TCG Related, and 4-Koma.
Main Game Adaptions
Isamu Akai and his adventures with is rude Clefairy
Spin-off Game Adaptions
Adaptations of Spin-off Games such as Pokemon Mystery Dungeon
A stylized adaptation of several select episodes from the Pokémon anime, although set in its own slightly different continuity
Movie Manga Adaptions
Direct adaptations of the Pokémon anime movies, sometimes with small changes in the story or Pokémon featured
Pokemon Mangas on any topic
ex: Magical Pokemon Journey A girl's oriented romance manga featuring the romantic lives of several trainers and their Pokémon
Pokemon TCG Related
Manga about children in the real world who compete in playing the Pokémon Trading Card Game
Gag comic strips layed out in four panels all the same size
Basically Mangas are Asian comic books you read backwards, which means you will have to pay to get one.