When you shop for a high-definition television, you may see the video image described as 720p, 1080i or some other combination of a number and a letter. These are used to describe the television’s video resolution.

 
What do these mean?

 
The number refers to the number of horizontal lines that are displayed in a complete screen image (a frame). Regular, standard definition TV in North America has 480 horizontal lines/frame. Some of the common high-definition TV standards are 720 and 1080 lines/frame.

The letter ("i" or "p") following the number refers to the way that the image is electronically created. There are two methods, interlaced and progressive. An interlaced image is electronically drawn in 2 passes--all of the odd numbered lines are drawn, and then all of the even numbered lines are drawn. Regular TV in North America is interlaced. A progressive image is drawn in one single pass.