UDF may refer to any of the following:
1. Short for Universal Disk Format, UDF is a file system first developed in 1995 by OSTA (Optical Storage Technology Association) and is commonly used with CD and DVD drives. UDF is supported on all operating systems, which allows a CD created on a Windows machine to be readable on a Macintosh machine.
2. Short for user-defined function, UDF is a function that can be modified to fit the user's needs.
3. Short for user-defined font, UDF is a font specified by the user and not the software program.