Emulator

An emulator is a computer program that allows someone to play a game. These programs aren't exclusive to computers, as some games, like Animal Crossing, have an emulator within the game's programming to allow the player to play older games. However, for the most part, gamers use emulators on their computers to play classic or otherwise unavailable games.

How LPers use emulators
Some Let's Players use emulators to make their LPs when they feel it would otherwise be impossible to do that game. Most of the time, the games that LPers use emulators for are Game Boy and DS games, usually Pok é mon  though bigger LPers, like Chuggaaconroy have used emulators to play games in the Mother series.

Controversy
The legality of emulators is questionable. While it's generally assumed that it's legal if someone owns a copy of the game he/she is emulating, it can still be argued that emulators are a form of piracy, especially when considering the people who do not own the games they emulate. For this reason, many LPers prefer using capture cards alongside the online game database on their game system of choice.