High-definition television (HDTV) is a television broadcasting system with a significantly higher resolution than traditional formats (NTSC, SECAM, PAL). While some early analog HDTV formats were broadcast in Europe and Japan, HDTV is usually broadcast digitally, because digital television broadcasting requires much less bandwidth. HDTV technology was first introduced in the US during the 1990s by a group of electronics companies called the Digital HDTV Grand Alliance.

In the 2000s, a number of high-definition television standards are competing for the still-developing niche markets. Current HDTV standards are defined by the International Telecommunication Union (ITU-R BT.709) as 1080 active interlace or progressive scan lines, or 720 progressive scan lines, using a 16:9 aspect ratio. HDTV is also capable of "theater-quality" audio because it uses the Dolby Digital (AC-3) format to support "5.1" surround sound.

The term "high-definition" can refer to the resolution specifications themselves, or more loosely to media capable of similar sharpness, such as photographic film. Currently, approximately 48 million households have HDTVs

Notation

In the context of HDTV, the formats of the broadcasts are referred to using a notation describing:

1. The number of lines in the vertical display resolution.

2. Whether progressive scan frames (p) or interlaced fields (i) are used.

3. The number of frames or fields per second.

The format 720p60 is 1280 × 720 pixels, progressive encoding with 60 frames per second (60 Hz). The format 1080i50 is 1920 × 1080 pixels, interlaced encoding with 50 fields per second. Often the frame or field rate is left out, indicating only the resolution and type of the frames or fields, and leading to confusion. Sometimes the rate is to be inferred from the context, in which case it can usually be assumed to be either 50 or 60, except for 1080p which is often used to denote either 1080p24, 1080p25 or 1080p30 at present but will also denote 1080p50 and 1080p60 in the future.

A frame or field rate can also be specified without a resolution. For example 24p means 24 progressive scan frames per second and 50i means 25 interlaced frames per second, consisting of 50 interlaced fields per second. Most HDTV systems support some standard resolutions and frame or field rates. The most common are noted below.