It's called handoff.
"When your Mac computers and iOS devices are within Bluetooth range of each other (about 33 feet or 10 meters), they can automatically “hand off” what you’re doing from one device to another. For example, you can start writing an email in Mail on your iPhone, then instantly pick up where you left off in Mail on your Mac."
Turn off Handoff
On a Mac: Choose Apple menu > System Preferences, click General, then deselect “Allow Handoff between this Mac and your iCloud devices.”
On iPad, iPhone, or iPod touch: Go to Settings > General > Handoff & Suggested Apps, then tap to turn off Handoff.