It's a combo console: a tablet that resides in a docking station. But you can lift the tablet out and take it on the road. Snap on the "Joy-Con" side controllers, and you don't need to cover the screen with your fingers, as you do on an iPad.
From Nintendo's press release: "One player can use a Joy-Con controller in each hand; two players can each take one; or multiple Joy-Con can be employed by numerous people for a variety of gameplay options."
Third-party support has long been Nintendo's achilles' heel, but it looks like the company has some notable names on board for the Switch, including Activision, Sega, Konami, Capcom, Bethesda and Square Enix.