File types: Text vs Binary
For Binary files you need a special application to "look" at their content. For example the Excel and Word programs for the appropriate files. Some image viewer application to view all the images. VLC to look at an mp4. Some application to hear the content of mp3 files.
- Text: .txt, csv, .py, .pl, ..., HTML , XML, YAML, JSON
- Binary: Images, Zip files, Word, Excel, .exe, mp3, mp4