Enhanced Definition Television
Marketing term invented to describe monitors which are slightly better than a 1970's SDTV set (i.e. less than or equal to 720x576 @ 60 Hz interlaced) and HDTV (i.e. 1280x720 @ 60Hz progressive up to 1920x1080 @ 60Hz interlaced.).
So the approximate boundaries of this marketing term include any television with more than 576 lines and a scanning rate greater than 60 Hz, and less than 720 lines (or 1280 horizontal pixels in the case of an LCD/plasma). This describes any CRT television designed in the last 15 years, and most LCDs for analog television.
Some EDTV sets are not just relabeled SDTV sets. They are actually failed HDTV sets, they were designed to support the minimum HDTV spec, but undershot the target. They are still being sold while the manufacturer redesigns and retools to the specifications.