These days, most of us have at least one HDMI cable plugged into our TVs. The ubiquitous accessories started appearing when HD television sets were introduced to the consumer market. So, it should be no surprise that the "HD" in HDMI stands for the same thing as it does in HDTV—"high-definition." High definition is the standard resolution that improved upon the standard-definition resolution used by most TVs at the end of the 20th century, and it generally means a resolution of 720p or higher.

The full acronym HDMI stands for "High-Definition Multimedia Interface," and it does precisely that — serving as a transmitter of uncompressed digital signals from one source of audio/video to another. It was developed by TV and home media hardware developers Hitachi, Matsushita, and Sony because traditional connectors, like the red, white, and yellow RCA cables — which you may have used to attach your VCR to your standard-definition TV — could not support the higher resolution of the HD era.

The red and white RCA cables provided left and right audio signals for stereo, while the yellow cable transmitted the video signal. HDMI, on the other hand, carries both video and audio signals through a single cable — and, in some cases, Ethernet — using multiple pins at each end, streamlining the mess of cables you may have found behind your TV. When using or purchasing an HDMI cable, you may notice it has a number after it. These HDMI numbers refer to the maximum resolution and refresh rate a given cable can support and currently range from 1.0 to 2.2 as improved standards are developed. Since both resolution and refresh rate affect the picture quality of your TV, it's important to understand what each number signifies.