HD or High Definition and SD or Standard Definition are two terms used to refer to television sets that use two different types of resolution. HD tends to have higher resolution than SD. As a result of this, HD TV sets are capable of producing images in an enhanced picture quality format. From top to bottom, HD television sets tend to contain 720 rows of pixels.
At times, they can also have up to 1080 rows of pixels, whereas the pixels in SD television sets are not as high as that of HD TV sets; they usually contain 480 rows of pixels. Although, you might not easily notice this difference if what you have in front of you is a very small TV set. In order to enjoy the quality image from an HD TV set, you must use it together with an HD video signal. The same thing is applicable to SD.