Apple Article - Use Continuity to connect your iPhone®, iPad, iPod touch, and Mac
Continuity allows seamless movement between your iPhone, iPad, and Mac, or when using them together.
Continuity features connect iPhone with your iPad, iPod touch so they can work together as one. You can start an email or document on an iPhone, for example, and then pick up where you left off on your iPad. You can use your iPad to make phone calls through your iPhone.