From Bulbapedia, the community-driven Pokémon encyclopedia.
An example of a Pokémon Prime
Pokémon Prime are a variant of Pokémon found in the Pokémon Trading Card Game. They first appeared in HeartGold & SoulSilver as one of two replacement variants for Pokémon LV.X. Pokémon Prime differ to other variant Pokémon in that they have no specific ruling or mechanic affecting their use: they are regularly classified as either Basic Pokémon, Stage 1 Pokémon or Stage 2 Pokémon and retain their regular names. The only difference, in terms of gameplay, is that they are considerably more powerful than their regular counterparts. Their card designs are also slightly different to others and, as with other considerably rarer cards, have a holographic border and name.
Pokémon that have appeared as Pokémon Prime