Desktop
In short: Desktop means the work surface of an operating system or a stationary computer as opposed to mobile devices.
In more detail: On the desktop lie icons, windows and the taskbar. “Desktop app” means a program for Windows, macOS or Linux.
In Depth
Comparison to mobile
Larger screen, mouse and keyboard, more power. Pages should adapt to both (responsive design). See mobile, app, desktop PCs, operating system.
See also: Mobile, App, Desktop PCs, Operating System (OS)