The original Pokémon TCG Base Set contained 102 cards.
Base Set was the English name for the first major English Pokémon Trading Card Game set. It was released in the United States on January 9, 1999, after the Japanese 1st Starter & Expansion Pack had launched in 1996. The set introduced the card game to a huge English-speaking audience.
Its 102-card checklist included Pokémon, Trainer cards, and Energy cards. The Pokémon featured were drawn from the original generation, including iconic cards such as Charizard, Blastoise, Venusaur, and Pikachu. Different printings can create collecting variations, but the standard Base Set checklist is counted as 102 cards.
A common mix-up is confusing the set size with the number of Pokémon in the first games. The original video games featured 151 species, whereas Base Set was a card expansion with a much smaller and differently categorized checklist.