Are the terms screen and the monitor in computer graphics used interchangeably?
The terms screen, monitor, and display are used more or less interchangeably to refer to the real-world physical device that shows the image you're looking at. (They're not 100% interchangeable: monitor means a discrete display device such as you'd use with a desktop PC. However, a built-in display such as the one in a laptop, tablet, or phone is never called a monitor.)

The image plane means the abstract geometric plane that identifies the surface of the display, but extends infinitely in all directions, i.e. isn't bounded by the edges of the display. The viewport or viewing window is the rectangle within this plane that identifies the edges of the display (or more generally, the edges of the image you're rendering, in case your app is running in a window and not fullscreen).

The term screen might also be used more colloquially to mean various other things, such as: various coordinate systems on the image plane ("screen space"), the viewport or view frustum ("the object is off-screen"), the back buffer ("render it to the screen"), and probably more.