What does `scan` mean in CSS Media Queries?

What exactly does the scan media features values progressive and interlace do exactly in simple terms? And are these the only values available for the sca开发者_开发知识库n feature?

They have to do with the output method of the screen of the device.

Describes the scanning process of television output devices.

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progressive and interlace are the only two possible values.

Progressive Scan

Progressive (or noninterlaced scanning) is a way of displaying, storing, or transmitting moving images in which all the lines of each frame are drawn in sequence.

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Interlaced Scan

Interlaced video is a technique of doubling the perceived frame rate of a video signal without consuming extra bandwidth. Since the interlaced signal contains the two fields of a video frame shot at two different times, it enhances motion perception to the viewer and reduces flicker by taking advantage of the persistence of vision effect.

Source.

It is used in style sheets for television. More info (book excerpt) here. If Interlaced and progressive videos interest you in some way, you can read about it here.