Top-down perspective is exactly as it sounds. The game is viewed looking down, as if the "camera" were hovering over the game itself. The genre that uses this perspective the most is the strategy game genreboth turn-based and real-time versions. This is because of all the minute micro-management details and tactical placement of troops on a landscape for battle. The player must be able to access the units and survey the situation with one glance. Good examples of top-down games are the various Pokémon games for the GameBoy and Monkeystone's Hyperspace Delivery Boy! for the PC and PocketPC platforms.
Non-strategy games that use this perspective include older Ultima and Zelda games, and many classic 2D games of yesteryear, including the arcade hits Centipede and Frogger.
Nintendo's Pokémon Crystal for the Game Boy platform utilizes a top-down perspective. (Used with permission by Nintendo of America, Inc.)