The original Japanese Pokémon games used the name Pocket Monsters.
The franchise began with the Japanese role-playing games Pocket Monsters Red and Pocket Monsters Green, released for the Game Boy in 1996. The Japanese title was later shortened internationally to Pokémon, a contraction derived from Pocket Monsters.
The original name remains visible in several parts of the franchise’s history. Japanese game titles, the anime’s original branding, and the first film’s Japanese title all use Pocket Monsters in some form. International versions instead adopted Pokémon as the familiar global name.
This is not the same as saying that Pokémon was created as a separate Western concept. The games, creatures, and core premise originated in Japan; only the branding was adapted for international markets. The shorter name helped make the franchise easier to use across games, television, cards, films, and merchandise.