filename extension; file extension
Computing term for the suffix after a dot in a filename, indicating file type.
Files with the filename extension '.txt' are text files.
Changing the filename extension may make the file unable to open.
拡張子 alone also means 'extension', but ファイル名拡張子 explicitly refers to the filename part.
Compound of ファイル名 (filename) and 拡張子 (extension).