What The Term "Progressive Scan" Means
In other words, in progressive scan, the image lines (or pixel rows) are scanned in numerical order (1,2,3) down the screen from top to bottom, instead of in an alternate order (lines or rows 1,3,5, etc...
followed by lines or rows 2,4,6).
By progressively scanning the image onto a screen every 60th of a second rather than "interlacing" alternate lines every 30th of a second, a smoother, more detailed, image can be produced on the screen that is perfectly suited for viewing fine details, such as text, and is also less susceptible to interlace flicker.
For a more comprehensive look at Progressive Scan, read my article: Progressive Scan - What You Need To Know.