Files are called files on Macintosh, PC, and UNIX systems. Folders are called directories on some systems. Word processing programs store documents in files. Spreadsheets are files. HTML pages are files.
Databases are files.
Your email in-box is a file. Software is stored in files. Everything on a computer is stored in files. I have 36,476 files of my own at the Statistics Department. Sometimes, the material to be stored is too complex to store in a single file and multiple files are used.