Aspect Ratio

Aspect ratio is the size of the image you are watching. The main two aspect ratios are fullscreen (4:3) and widescreen (16:9). Since the 1950s, most films have been shot in widescreen. However, when shown on a 4:3 TV set they are often panned and scanned so they can fill the image. This means only a 4:3-sized portion of the widescreen image is shown, usually where the main action in the frame is taking place, which pans to keep this portion in the frame:

This completely cuts off the rest of the image, ruining the composition of the shots and potentially causing the audiences to miss vital elements of the frame. The best way to show widescreen images of fullscreen TVs is to show them letterboxed, which preserves the image with black bars at the top and bottom of the screen:
When a 4:3 image is displayed on a widescreen TV it is often stretched to fill the screen, making the image appear stretched. The best way to show the image is to have it pillarboxed with preserves the image with black bars on either side.

TV Pixels:

A still image is made up of pixels which your brain assembles into an image. The quality or resolution of the image increases with the amount of pixels you have.

TV Motion:

TV is a series of still images which are played one after another at a fast speed to give the illusion of one fluid moving image. The standard speed for British TV is 25 frames per second

The TV Screen:

Moving images are divided into horizontal lines of pixels called scan lines, which are transmitted to televisions. British TV shows 525 rows.