Enter a clue or pattern or both:
The Clue
They have extensions (9 letter answer)
The Answer
FILENAMES
Tags
Notes
The answer FILENAMES is so rare that it appears less than once every 2500 puzzles.
Definition
FILENAME as a noun:
1. (filename, file name, computer filename, computer file name) = (computer science) the name given to a computer file in order to distinguish it from other files; may contain an extension that indicates the type of file