What is continuity and "Handoff" in iOS 8?

Continuity between iOS and OS X devices was a major concept during the iOS 8 presentation at this year's WWDC. It basically refers to the connectivity between one's devices and the capability of passing off tasks between them. Apple placed a lot of emphasis on this in the development of iOS 8 and OS X Yosemite. While not a whole lot is known at this point, we do know some features from Apple's iOS 8 preview.

The "Handoff" feature will allow a user to start using an app on one device and then pick up where he/she left off on another. For example, you might be browsing with Safari on your iPhone, walk into your office and pick up browsing on your iMac right where you stopped on your phone. The same applies to many other apps including Mail, Messages, Notes, Calendar, Numbers, Maps, Pages, Keynote, Contacts and Reminders. Developers can also add Handoff functionality to their apps.

Additionally, the continuity features will also allow you to answer (and make) calls from any of your devices that are connected to the same Wi-Fi network as your iOS 8 iPhone.

There is also an "Instant Hotspot" feature that you can enable on your iPhone, allowing your phone to become a Wi-Fi hotspot for your other devices.