The concept of the second-person perspective can take two meanings depending on where it is used. In literature, second-person perspective is characterized by the use of second-person pronouns, such as "you". This perspective is used when the main character is the person reading the book (or playing the game). Perhaps this perspective's best known use is in choose-your-own adventure books and tabletop role playing games like Dungeons and Dragons.
There are two main types of second-person perspective seen in games; text-based, and camera-angle based. With new ways to interact with games, a 3rd type which is consistent with the Text type and narrative definitions but Graphical, where you are the Hero.
In video games, this kind of second-person perspective is mainly seen in text-based adventure games, such as the Zork series and Hitchhiker's Guide to the Galaxy, as well as early visual novels like Portopia Serial Murder Case.
It can also be seen in some role-playing games to explain an action that the player character has performed, for instance: "You use Magic Missile on the trolls". The use of second-person perspective can help players feel as if they are actually the character they are controlling.
The other type of second-person perspective in games has to do with camera angle. In this type of second-person perspective, the main character (the on being controlled by the player) is seen through the perspective of another character.
For instance, the first boss of Battletoads has the player fight the boss through the eyes of the boss. The player is still in full control of the main character (as being able to move the main character, mind control does not count), but all the action is seen through the boss's perspective.
Super Mario 64 was one of the first games where all the action is seen in a second-person perspective, through the camera of Lakitu.
You (Real You) are the Hero
Games such as Fruit Ninja using XBox 360 Connect are played where the person playing the game is the Hero and action is seen through the eyes of You and not through a character within the game itself (such as is the case typically with a First Person Shooter). Several Light Gun games also fall into this category in addition a couple of SONY Eye Toy Camera based games.