GTS = Global Trade Station (System) — Nintendo Wi-Fi Connection service (Gen IV: Diamond/Pearl/Platinum/HeartGold/SoulSilver; Gen V: Black/White/Black 2/White 2). Shut down May 20, 2014 (WFC closure).
Summary: GTS was the first global async trade system. Replaced by Pokémon Home. On original carts — dead without custom servers.