HD refers to cameras with a standardized resolution of 720p or 1080p. The numbers 720 and 1080 refer to the horizontal resolution. HD is a type of megapixel camera. All HD cameras are megapixel but not all megapixel cameras are HD. While standard definition cameras (e.g., analog cameras and 4CIF IP cameras) have no more than 400,000 pixels, all megapixel cameras (including HD) have 1,000,000 or more pixels. 1080p (1920×1080 progressively displayed pixels; also known as Full HD or FHD, and BT. 709) is a set of HDTV high-definition video modes characterized by 1,920 pixels displayed across the screen horizontally and 1,080 pixels down the screen vertically; the p stands for progressive scan, i.e. non-interlaced. HD or High Definition is pretty much the industry resolution streaming standard. The resolution refers to a pixel height of either 720 or 1080 pixels. HD is further categorized into HD-ready or standard HD resolution of 720p and 1080p or 1080i full HD resolution. A camera with 10-20 megapixels is going to, in most cases, be more than capable of meeting all your needs. You’d be served far better by saving money on your camera and investing in better lenses.