What was the original Japanese name used for the Pokémon game series?

The original Japanese name of the Pokémon game series was Pocket Monsters.

In Japan, the first games were titled Pocket Monsters Red and Green. The shortened international name Pokémon comes from the romanized Japanese title Poketto Monsutā and became the standard branding used around the world.

The name reflects the series’ central idea: portable creatures that can be collected, trained, traded, and used in battles. The Game Boy was especially important to that concept because its link cable allowed two players to exchange Pokémon.

The television series and other products also used Pocket Monsters in their original Japanese branding. English-speaking markets generally adopted Pokémon instead, partly because “Pocket Monsters” was already associated with other trademarks in some regions. The two names refer to the same franchise, not separate series.