As you may be aware that every receiver (I mean Digital) has a microprocessor that executes a program (software). This software has to be stored in some non-volatile media. For this purpose, they use Flash Memory for storing the software (program) and other information (like channels list, satellites list, transponders list etc.) that has to be retained even when the receiver is powered off. The software that is written into this memory (Flash) is commonly being called as "Flash File". This can be anything from whole software or just the channel lists, or even the keys files that can be selectively written or read from th flash memory. But in common terms, a Flash File means the software that is an image of the entire contents of the Flash memory. It is always a good idea to keep a copy of Flash file for your receiver. This could be used for reviving your receiver in case something goes wrong at the time of upgrading software, or other unfortunate events like that.