Standard-definition television (or SDTV) is a television system that has a resolution that meets standards but not considered either as enhanced-definition television (EDTV) or as high-definition television (HDTV). The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as analog systems. In the USA, SDTV refers to digital television broadcast in 4:3 aspect ratio, the same aspect ratio as NTSC signals. When a television set is labeled "SDTV", this means that the set includes an ATSC tuner, but scans its picture in the same 480i pattern used in NTSC.
In the PAL standard SDTV usually refers to a 576i signal.