Stands for "High-Definition Video." According to a consortium of manufacturers including Sony, JVC, Canon, and Sharp, it is a "consumer high-definition video format." HDV is the next step up from Mini DV, which has been used in consumer digital camcorders for several years. The HDV technology allows high-definition video to be recorded on a Mini DV tape, using MPEG-2 compression.
Of course, recording in high-definition requires an HD camcorder, such as the Sony HDR-FX1 or the JVC GR-HD1. These cameras are significantly more expensive than their Mini DV counterparts, but can capture much higher quality video. HDV uses a native 16:9 widescreen format, with a resolution of 1280 x 720 pixels. This is a substantial improvement over Mini DV, which records video in a 4:3 format, with a maximum resolution of 500 horizontal lines. Most HDV camcorders allow the user to record in standard DV as well, but if you shell out a couple thousand dollars extra for a HDV camcorder, you might as well shoot everything in HD.