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HDA prefix used to designate a star as listed in the Henry Draper Catalog.
On drawings, abbr. for head.
HD(1) See HD Radio and HD audio.
(2) (High Definition) HD often refers to a high-resolution digital TV (see HDTV). The HD designation is also used with many TV/video formats (see HD analog formats and HD formats).
(3) (Hard Disk, Hard Drive) For example, a 500GB HD is a 500 gigabyte hard disk. FD means floppy disk; now a distant memory. See hard disk, magnetic disk and floppy disk.
(4) (High Density) HD and DD (double density) were used in floppy disk designations. For example, 3.5" 1.44MB HD and 720KB DD or 5.25" 1.2MB HD and 360K DD. See floppy disk.
(5) (High Definition) A screen resolution of 1280 x 720 pixels. HD+ is 1480x720. See DTV, FHD, 720p and screen resolution.
|HD and HD+ Screen Resolutions|
|In the Galaxy S7 smartphone (top) and S8 (bottom), the screen resolution can be reduced to save battery.|