A smart hub allows to manage all your wirelessly connected smart home gadgetry - smart locks, thermostats, room sensors, switches, lights, cameras, smoke alarms, leak detectors and more.

A smart uses a centralized app to control all these devices.

Good smart hubs are reasonable priced. They are compatible with more third-party devices, and supports all the major wireless protocols relied on by smart devices. 

However, these are early days for the smart home / smart hub concept. Thus, these are early-stage devices.

The best smart-home hub: Samsung SmartThings Hub (multipurpose)

The best user-friendly smart hub: Wink Hub (widely compatible)