High definition video
High definition video is a set of moving pictures that is of a higher resolution relative to other content at any given time.
Television broadcasts transitioned to digital around 2008.
Satellite, digital cable, and fiberoptic television service are all capable of high definition, though they usually charge extra to get all of the HD channels.
Blu Ray discs are high definition. DVDs are standard definition.
On television sets smaller than 30" it doesn't make much difference.