File Extension DIFF File Format Difference data file DIFF stands for Difference data file. This was last updated in March 2012 By Margaret Rouse Browse File Extensions Alphabetically: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Ask a Question. Find an Answer. Ask your peers a question about this file extension. Ask a Question what is the diff between cursor and plsql table Error with NTBackup and restore SETON LR and RETURN.