Energy cards (Japanese: エネルギーEnergy) are the cards that power Pokémon attacks in the Pokémon Trading Card Game. A Pokémon cannot attack without the required energy attached to it. Under normal circumstances, a player can attach one Energy card to one of their Pokémon per turn. There are two different classes of Energy cards: Basic and Special.
Basic Energy cards
Basic Energy cards (Japanese: 基本エネルギーBasic Energy) are defined as nine Energy cards that share their printed type with a Pokémon. They are the only cards that players are permitted to have more than 4 copies of in their decks (aside from Arceus which has its own Special Rule). Basic Energy cards always provide 1 of their printed type of Energy or 1 Colorless Energy, meaning that any basic Energy card can provide a Colorless Energy. There are no basic Energy cards that provide only 1 unit of Colorless Energy.
Note: The first Darkness and Metal Energies appeared in Neo Genesis but were considered Special Energy cards.
Special Energy cards
Special Energy cards (Japanese: 特殊エネルギーSpecial Energy) are cards that provide more than one Energy of a specific type and/or have an additional effect besides providing Energy. Some may heal the Pokémon they're attached to, add damage to their attacks, or may even provide several different types of Energy at once. A majority of them provide only Colorless Energy; however, there are several which provide one or more of any type of Basic Energy. Unlike Basic Energy cards, no more than four can be in one deck at a time.