Mobile hotspot refers to the ability to use cellular data as your internet connection.

The term is generally used in two ways:

Mobile hotspot device - is a small data only device, usually battery powered, which combines a router with a cellular modem allowing the user to share a cellular connection with other nearby devices via a Wi-Fi connection. Also known by their branded names of MiFi, Jetpack or Aircard.

Personal Mobile Hotspot - is a feature on a smartphone that allows you to share its data connection with other devices.

Sometimes this term is also called 'tethering' - which usually refers to using this same feature but over a physical USB cable instead of wirelessly.