Home Theater Projector Resolutions: 720p (1280x720 pixels, 16:9 aspect ratio): This format is most commonly used for economical movie projection. It matches the 720p HDTV standard. 1080p (1920x1080 pixels, 16:9 aspect ratio): This is now the standard format for home theater. It matches the 1080i/1080p HDTV broadcast and Blu-ray formats.
The best home theater projector is the Optoma UHD50. This projector hits a sweet spot, by combining 4K resolution, excellent color accuracy, and very high brightness, at a price that no TV can hope to match.
HD is, of course, an acronym for High Definition. In the projector world, primarily HD is a phrase associated with home theater projectors, rather than other types, but recently, the HD definition is showing up on business, education and other commercial projectors with 2K resolution. (2048×1024, or similar).