While there are a number of different quality levels of digital television programming, three are most common:
Standard Definition Television (SDTV) SDTV is the bottom tier of quality for both analog and digital broadcasts. SDTV may be transmitted in either traditional (4:3) or widescreen (16:9) format.
Enhanced Definition Television (EDTV) EDTV is of better quality than SDTV, and is broadcast in 480p widescreen (16:9) or traditional (4:3) format.
High Definition Television (HDTV) Widescreen (16:9) HDTV provides the best picture and sound quality available in digital TV broadcasts. There are several different grades of resolution within the HDTV range.