A screen is the portion of a display device, a surface on it, on which the images the device produces appear. There are many types of display devices which have screens. These include TVs, tablets, and, yes, monitors. So a screen is something a monitor has, but screens are not exclusive to monitors. In addition to the screen itself, all these devices have additional internal components which they use to convert received information into visible pictures. The amount of such additional hardware in a monitor tends to be about as minimal as it can get, because the information sent to the monitor already represents the picture explicitly. The computer to which a monitor is connected has already decided exactly what the picture should look like at every moment in time. In a TV or a tablet, there is additional work to be done to figure out what the picture on its screen is supposed to look like. A tablet is like having a computer built into a portable monitor. A TV must convert radio signals into moving pictures before they can be displayed on its screen. When you use a TV with a set top box, the TV is functioning more like a monitor and the set top box as a computer. Indeed, most modern TVs will function fine as computer monitors.