What Japanese title was used for the original Pokémon games?

The original Japanese title used for the Pokémon games was Pocket Monsters.

The Japanese franchise name is Poketto Monsutā, written in English as Pocket Monsters. Pokémon is the abbreviated international form, with an acute accent over the e to guide pronunciation. The shortened name became the universal brand for the games, anime, cards, films, and merchandise.

The first Japanese cartridges were officially titled Pocket Monsters Red and Pocket Monsters Green. When the franchise expanded internationally, the shorter Pokémon name was retained, and the Western game pairing became Pokémon Red and Blue.

“Pocket Monsters” is sometimes mistaken for a description created by English-speaking fans, but it was the original Japanese branding. The phrase also explains why the franchise's Japanese title and its international title do not look identical even though they refer to the same property.