Cortana is Microsoft's intelligent personal assistant that debuted in Windows Phone 8.1.
Cortana is an intelligent personal assistant in Windows Phone 8.1. She accepts both typed and spoken user input, including natural language queries, to provide information and perform actions on behalf of the user. For this purpose, Cortana can interface with a number of apps and web services, including Bing, Foursquare, Facebook and more.
Cortana is named after the fictional AI in the Halo series of video games, and is voiced by the same actress, Jen Taylor. When enabled, Cortana takes over the duties of the standard Bing Search app.