What do you understand by the term file name extension?

A file name extension is a suffix added to the end of a file name, separated by a dot. It is used to indicate the type or format of a file. The extension typically consists of three or four characters and is commonly used in operating systems to associate files with specific applications or to identify the file's content. For example, in the file name "document.docx", the extension ".docx" indicates that the file is a Microsoft Word document.