Lua is the industry standard for game programming. It is similar to JavaScript and Flash's ActionScript. Anyone who's done any scripting in these languages will make the transition to Lua almost immediately.
Lua has been useful in creating various applications and games. Many game programmers have found Lua to be a convenient scripting language due to how easy it is to embed, its fast execution, and its small learning curve. It is ubiquitous in World of Warcraft. It is also used by Electronic Arts, Rovio, ngmoco, and Tapulous in games such as Angry Birds, Tap Tap Revenge, Diner Dash, and so on.
For more information on Lua, refer to http://www.lua.org.