HD stands for High Definition. It is a method of displaying video digitally at much higher quality than Standard Definition (SD). The accompanying audio is also of a higher quality.
If you have a flatscreen TV, HD content will appear clearer and sharper than SD content because there are more pixels per inch on screen. This results in a better viewing experience for some shows.
There is no definitive standard for HD. Modern TVs are capable of playing video in a range of formats, which may include:
- 720p (HD Ready)
- 1080p (Full HD) or 1080i
- 4k or Ultra HD TV (UHDTV)
For more information, see the following topic: What's the difference between 1080p and 1080i?