Pokemon Labs are where Professors (Oak, Elm, Birch, Rowan, or Juniper) give you a starter pokemon.
Professor Oak in Pokemon Blue, Red, Fire Red and Leaf Green, either he gives you Bulbasaur, Charmander or a Squirtle, but in Pokemon Yellow he gives you a Pikachu.
Professor Elm in Pokemon Gold, Silver, Crystal,HeartGold and SoulSilver either he gives Cyndaquil, Chikorita or a Totodile.
Professor Birch in Pokemon Ruby, Sapphire and Emerald either gives you a Treecko, Torchic or a Mudkip,
Professor Rowan in Pokemon Diamond, Pearl and Platinum either gives you a Turtwig, Chimchar, or a Piplup).
Professor Juniper in Pokemon Black and White either gives you a Snivy, Oshawott or a Tepig.
Each Generation has 3 different starter Pokemon.