Cortana feature in Windows 10

Cortana is one of the signature features of Windows 10, adding a personality (with the name and voice taken from the Halo franchise on Xbox). Essentially, Cortana acts as a personal assistant, combining local and web search with the ability to understand spoken commands and enough smarts to convert those commands into tasks, appointments, or instructions.
20 Introducing Windows 10 for IT Professionals, Preview Edition 
Although Cortana has

been part of Windows Phone for nearly a year, she appeared for the first time in the Windows 10 Preview in late January. Because much of Cortana’s magical powers derive from webbased services, she’s getting smarter with age. What you see in the current preview releases is a pale imitation of what you’ll see after a year or two of continuous improvements. The best way to understand Cortana is to type something into the box just to the right of the Start button, or click the microphone icon and say it instead. (If you don’t enable Cortana, that box performs simple searches, sans personality.) After you and your users get past the novelty of it all, take a look at Cortana’s notebook, which is shown in Figure 2-5. That’s where you can fine-tune the information—news, upcoming appointments, weather, reminders, and so on—that pops up instantly when you click in the “Ask me anything” box. (That summary is replaced with search results as soon as you start typing.)