UDF may refer to any of the following:
1. Short for Universal Disk Format, UDF is a file system created in 1995 by OSTA (Optical Storage Technology Association) and is commonly used with CD (compact disc) and DVD (digital versatile disc) 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.