Megapixel is a new camera technology that provides resolution well above traditional surveillance camera technology.

The highest resolution traditional NTSC analog security cameras available, when recorded at the highest resolution available, would produce an image of 704 X 480 which is equal to 338k pixels which is roughly 1/3 of a megapixel.

The newer megapixel cameras by comparison start at 1.3 megapixel (1,300k) with 2, 5 and even 8 megapixel cameras becoming very common and affordable.

You can see a comparison of what an analog camera image looks like compared to a 2 megapixel image here: http://www.3xlogic.com/rsc/megapixel/megapixel-comparison.html