The ability to update the firmware / software of a phone over the phone network. Such updates usually fix bugs or glitches, although they can also add new functionality in some cases.
Both the phone and the carrier must specifically support FOTA, and support the same type of FOTA.
In some cases, the updates may be pushed to the phone automatically, while in other cases the user may be given a choice of whether to receive the update.
FOTA removes the need to take a phone into a store location or send it to a service center for updates. This adds convenience for the consumer and reduces cost for the carrier.
FOTA is sometimes referred to as just OTA.