Definition of file extension in English:

file extension

noun

Computing
  • A group of letters occurring after a period in a file name, indicating the format of the file.

    • ‘When I try to click these files, a window appears and asks me to select the appropriate file extension.’
    • ‘This is done by viewing the file extension in the email attachment.’
    • ‘The protocol name is simply the filename, excluding any file extension.’
    • ‘My best guess is that Ed has accidentally saved some images with the wrong file extension.’
    • ‘Have you ever gotten an e-mail from a friend with a file extension you may not be familiar with?’