CFW, also known as Custom Firmware, refers to an unofficial firmware which is created by modifying the firmware of a device. There are several synonyms for CFW, including custom software, custom OS, custom ROM, and hacked firmware. Custom software refers to a modified version of an operating system, application or software program whereas custom OS refers to an entire operating system which has been customized to meet specific needs. Custom ROM, on the other hand, is a modified version of the firmware of an Android device, while hacked firmware refers to a firmware that has been altered to bypass security measures in order to gain access to unauthorized features.