File with a .UDF extension contains a universal disc image, usually an optical data storage. It is a collection of files utilising a cataloguing structure, stored in a universal format and maintained by OSTA – Optical Storage Technology Association. This file format is often used for purpose of CD recording, however, utilising different extensions, specific for given software.

UDF files can be used for purpose of recording DVDs or CDs, or other optical data storage. This format allows to modify the content of target disc – deleting and modifying files, also after they are already recorded.