A small personal device that creates a small area of Wi-Fi coverage allowing nearby Wi-Fi devices to connect to the Internet. In other words, the device serves as a link between nearby Wi-Fi devices and a cellular data network.
The device may be a dedicated device that provides only this function, or this function can be built into a phone.
When it is built in to a phone, it may be offered as a distinct service that must be activated and paid for in addition to the phone's standard data plan.