File type

The specific kind of information contained in a file, usually designated with a file extension (e.g. .doc for a Word document; .txt for a text document, etc.). A .pdf file is common format for reports. Systems will usually expect a specific file type for input/output operations. Your election night reporting system may accept only a .txt file or a .zip file.

Source: Information Technology Terminology, U.S. Election Assistance Commission,