From Bulbapedia, the community-driven Pokémon encyclopedia.
Item cards (Japanese: グッズ Goods cards) are a classification of trading cards that debuted in Japan with the release of the HeartGold & SoulSilver Collections at the start of the LEGEND era. The English releases did not adopt this name change right away, and continued classifying them as Trainer cards until the release of Black & White.
Item cards, as the name suggests, depict items, typically from the Pokémon games, such as the Good Rod and Moomoo Milk, and any other non-Supporter/Stadium Trainer cards. Much like how Supporter and Stadium cards changed their colors to red and green, respectively, Item cards changed to blue.
Players are allowed to play as many Item cards as they wish during their turn. Many Item cards have seen multiple releases and illustrations since Item cards debuted in the HeartGold & SoulSilver expansion. There are currently 204 different Item cards, though many have been printed multiple times with different artwork.
List of Item cards