<font color='#000000'>Progressive scan basically means 'deinterlacing." The picture used by the NTSC standare (ie. regular TV) is 'interlaced', meaning every odd line is drawn, followed by every even. The fact that the picture looks like a continuous one is due to the phenomenon called persistance of vision. During scenes with a lot of motion the technique of interlacing introduces artifacts that detract from the picture quality (eg, jaggies, moire, stairstepping, etc.)
Prog scan basically compensates for this by deinterlacing the image and drawing the whole picture all at once. This creates a much more stable image, especially where motion is concerned.
That's the best definition I can muster; I'm not an engineer, just a regular guy!</font>