A mobile hot spot is a device that allows laptops, tablets and other devices to connect via Wi-Fi and provides a data connection using a cellular link. Some smartphones can do this, and there are a number of dedicated hot spots available from different carriers.
A hot spot establishes a data connection using its cellular radio, connecting via 3G, 4G, LTE or whatever standard is available. Once connected, it broadcasts a Wi-Fi SSID, effectively serving as a wireless router. Any Wi-Fi capable device within range can connect to the hot spot and through it, the Internet. Standard Wi-Fi passkey security can be used to keep unauthorized users out.
While some smartphones can serve as Wi-Fi hotspots, not every carrier allows this activity due to the increased amount of data transfer that may result. In some cases, the carrier may actively filter traffic looking for this activity, which is commonly known as "tethering" a device to a phone. Using tethering when a service provider expressly forbids it may result in extra fees or an interruption in service.
When carriers offer dedicated hot spots, they are generally connected to a special data plan that expressly allows tethering. In some cases, a carrier may allow a subscriber to add a hot spot to an existing data plan for a small monthly fee.