FOTA (Firmware Over-the-Air File)
The FOTA System file format
FOTA files are firmware files used by mobile phones and devices that run on the Android operating system. These files are used to upgrade different instances of Android, such as the theme, operating system, and other system data. Most commonly, FOTA files can be found on Samsung phones, but they can be found on other Android devices as well.
Technical details of FOTA files
The long name of the file is already an indication of the way how they are distributed. FOTA stands for Firmware Over-The-Air. A connection to any computer is thus not needed in order to upgrade the Android device in question. Instead, the FOTA files are delivered wireless during the system update. When upgrading a phone using FOTA files, Samsung vouches that no data is lost while doing so. Text messages, apps, images, and the like will remain untouched by the upgrade.