Viewport

In DCS and Helios, a "Viewport" refers to an area of the screen where DCS shows stuff. Usually, people use this term only when talking about additional viewports used to show controls on extra monitors, such as MFDs displayed on a second monitor. However, the main 3D view of DCS is also technically a viewport and so is the area of the screen used for the main DCS menus (the "UI"). So there can sometimes be some confusion as people refer to the term viewport.

Viewports are created by editing a Monitor Setup file and then selecting the name of this setup in the "Monitors" option of DCS' System Options. There are some monitor setups provided by DCS that also create additional viewports, such as "LMFCD + Camera + RMFCD." These create additional viewports with common names, like "LEFT_MFCD" in the example given.

If a DCS aircraft has a cockpit instrument ("device") that supports an external viewport with the same name, then it will find this viewport and show its data there. For example, most planes that have MFDs call the left one's viewport "LEFT_MFCD," so it will be shown if your selected monitor setup has a viewport with that name. If it does not have such a viewport, nothing happens.

Additional viewports (the ones that are not the UI view or the main 3D view) as frequently called "viewport exports" or "exported viewports" or just "exports" which is also confusing, because "export" means multiple unrelated things in DCS (see export.lua).