The original Japanese title of the Pokémon franchise was Pocket Monsters.
In Japan, the first games were released as Pocket Monsters Red and Green. The English name Pokémon is a contraction of “Pocket Monsters,” reflecting the idea that players could carry a collection of creatures in portable game cartridges and train them anywhere.
The Japanese title was shortened internationally partly because the phrase “Pocket Monsters” was considered too generic and could create naming conflicts. The accented é in Pokémon helps distinguish the franchise's official name in English-language markets.
The name also explains why the series' creatures are called Pokémon rather than monsters in most contexts. “Pokémon” functions as both singular and plural in official usage, although everyday speech often uses “Pokémon” for one creature and “Pokémon” for multiple creatures as well.