Open frame monitor is an installation type of touch screen monitor. Usually normal monitor is with vesa hole to mount bracket, wall mount bracket or desktop stand. But open frame is a metal backcase for touch screen monitor, it is with some holes onside the frame to set the screws. 

Put a cabinet before the open frame monitor, and locking the metal frame with the holes on the surrounding frame. Which is the installation methods of open frame monitor. And we can see this from the arcade machine.

There are many equipements in casino like this, people would like to play arcade games such as POG, WMS, Bally, IGT and so on. So the arcade machine is also various type, the requirement of open frame monitor is different. Someone uses 19 inch square touch screen to be arcade table, someone applies big touch screen monitor to fishing machine, someone requires 9:16 rotatble screen. 

Of course, the above machines is generally for gambling, the open frame monitor is also could be applied to MAME, ATM, advertising display, etc.