An image resolution is known as the "sharpness" of the screen's image. It is measured by how many pixels it can hold vertically and horizontally. [Dictionary.com] The more pixels it is able to hold the greater the brightness and sharpness of the images and colors.
A pixel comes from the phrase a "picture element". The pixel is the smallest image on the screen. Each pixel is managed individually and each can hold a different shade of color and the intensity of brightness. [PCGuide.com]
"In the picture below it shows a close up of a "square" pixel in solid colors." [Digionary.com]
When pixels reach into the millions, they are known as a megapixel. For example, if you have a resolution of 1600x1200 pixels it is also known as 1.9 megapixel; to convert the pixels to megapixel you multiply the vertical and horizontal rows and divide the answer by one million then round (1600 x 1200 = 1,920,000 / 1,000,000 = 1.9). Megapixel are not used just for the resolution of pixels on a screen but also for the number of image sensors of a digital camera or the number of display elements of digital displays. [En.Wikipedia.org]
In the video below it shows 8 bit pixels taking over New York City. If you don't think resolution on our screens have drastically changed over time, this video will show the change with the help of characters from the 1980s arcade and video games. [YouTube.com]
References:
Dictionary.com, Jan. 27, 2001 (http://dictionary.reference.com/browse/resolution) PCGuide.com, Jan. 27, 2011 (http://www.pcguide.com/ref/video/modesPixels-c.html)
Digionary, Jan. 28, 2001 (http://www.digionary.com/)
En.Wikipedia.org, Jan. 27, 2011 (http://en.wikipedia.org/wiki/Megapixel#Megapixel)
YouTube.com, Jan. 26, 2011 (http://www.youtube.com/results?search_query=pixels%20by%20patrick%20jean&search=Search&sa=X&oi=spell&resnum=0&spell=1)
