Maybe in your case, this is something like a remote desktop server or a program ... If one of these lacks the option to show a menu bar icon in lieu of a dock icon, this can result in your dock ...

The dock on a Mac computer allows you to select applications for quick access along the bottom of your screen. From web browsers to favorites such as Pages and iTunes, you can customize your dock ...

If the app was minimized, clicking its Dock icon restores the window to its previous size and location on screen. The Windows counterpart is the Taskbar (see Win Taskbar). Introduced with Mac OS X ...