The desktop environment (DE) includes the Application menu (usually something like the Start Menu on Windows), task bar or application switcher, and basically anything you can see before you open any programs. A simplified name for a DE I often use for novices is a "menu system". Usually the DE also has its own preferred applications of various sorts. The preferred applications are usually displayed with a generic name such as "File Manager" "Text Editor", "Image Viewer" etc. for ease of use but the specific project names may be hidden, such as "Caja", "Pluma", and "Eye of MATE" respectively. Proprietary operating systems like Windows or macOS may make surprise changes and they are more difficult to customize (especially with regard to default programs). You may not want to customize it, but if the corporation such as Microsoft or Apple changes it in a way you don't like, you have an uphill battle. On GNU+Linux systems, you can choose which desktop environment is best for you, and mix and match free software as the preferred applications.
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