MiFi is a portable broadband device that allows multiple users and mobile devices to share a 3G or 4G mobile broadband Internet connection and create an ad-hoc network (a Local Area Network built spontaneously as devices connect).
MiFi is often used as a generic label for any device that can be used as a pocket router or personal hotspot. This name is thought to stand for "my Wi-Fi." Some 3G/4G carriers sell MiFis with pay-as-you-go plans, while others require either a monthly fee or an annual contract.
Even though some smartphones can be used as hotspots, they lack management capabilities offered by MiFi, such as controlling data consumption on connected devices. In addition, the phone user must turn the hotspot feature on whenever sharing is desired, and the phone itself cannot behave like a Wi-Fi device during this period.