Pokemon Prime is a subcategory of card that first debuted in HGSS. They're standardly much more powerful versions of the regular Pokemon, with no significant drawbacks.
Here is an example: http://pokebeach.com/scans/heartgold-and-soulsilver/107-donphan.jpg
The artwork of the Pokemon's face is zoomed into the camera, and they are much stronger than normal Donphan (120 HP on a Stage 1?). The 'Prime' isn't part of the name, so you can only have 4 total of that Pokemon species in a deck.
