What is it and why should I care??
Monitor Calibration is CRITICAL for anybody who is entering Image Competition, as proper calibration will make sure that Whites, Reds, Blues and every other color on your monitor match the Whites, Reds, Blues and every other color on the Image Competitions Judging Monitor, or to put it simply, the judges see the image on their monitor as you see it on yours.
A monitor is a monitor is a monitor - but there are many factors that alter the way a monitor displays an image, think of walking into ANY electronics store and looking at the GREAT WALL OF TV's, and look at how the same picture, played at the same time looks so different one each and every screen in the same environment. These displays have not been calibrated.
When you first calibrate your monitor it will likely look dull and 'Brown' - but do not fear your eye's will quickly adjust. This will help not only in image competition but also in printing your work as every 'Lab' printer also works from the calibration schema.
Common makers of inexpensive Calibration devices are X-Rite, Spyder and many others.