Why are the terms "progressive" and "interlaced" still used with LCD/plasma flat panels?

If flat panel LCD/plasmas don't use interlaced or progressive scanning techniques, but rather display an entire field at once, why are the terms interlaced and progressive still used when referring to their resolution? Is it more referring to the type of signal being input, rather than the way the panel is displaying the image?

Flat panel displays (both LCD and Plasma) are progressive displays by deffinition. They display the entire frame of an image and refresh it a some given rate.

The terms interlaced and progressive are often used to designate a type of signal being sent to the TV, such as 1080i, 1080p, 720p, or many others. An 1080i signal means you get half the image at one instant and the other half at the next often refreshed at 60hz. 1080p signal means you will get a whole image refreshed at 30hz.

Now to put it all together. If your TV has a resolution of 1080p, then when it recieves a 1080p signal it has to do little to no processing on it to get it to display. But when it gets a 1080i signal it must de-interlace it, effectively changing the 1080i60 signal into a 1080p30 signal, because flat panel TV's are progressive.

That refers to the type of signal they accept as input. If a set uses a 1080p or 720p display, it will accept 1080i and 480i (interlaced formats) as input and convert them to 1080p for display. However, many 1080p sets will not accept 1080p signals as input (now available from some high-def DVD players and game consoles through HDMI connection).