frame

I've come across this simple definition of a frame. It's simple, but yet I find it beautiful and poetic:

"The camera and the lens work together to record a particular horizontal rectangle of reality. The    rectangle is only a small segment or cut out window of the total sphere of the physical world around the camera operator. This cutout has a finite and defined border, called the frame." 

Thompson, Roy & Bowen, Christopher J. (2009), Grammar of the shot. 2nd ed.Oxford: Elsevier.