It’s the wire that goes from your cable or satellite box to your TV. The HDMI cable was created to please everyone from major movie studios to impatient spouses. For the most part it does a good job.
In the early days of HD, back in the 2000s, you had two choices for connections. Component connections took at least five cables to go from your box to your TV. If you had surround sound you were looking at nine cables. Yes really. This was not so popular with home theatre fans who wanted a clean installation. Their other option, the DVI connector, was really delicate and tended to break.
At the same time, the signals that travel over these old connections aren’t copy protected and that made the movie studios mad. They didn’t want you hooking up a video capture device and copying movies to your hard drive… because you might sell them for less than the studios could. Something had to be done.
The HDMI Cable came into being in the mid-2000s to address all these problems. The one, easy to plug cable carries video and audio and uses a really fancy tap-dancing scheme to make sure that copy protected content is safe. It took a few years for everyone to figure out how to do it right, but HDMI is now the standard for all HD devices.
The best part about HDMI cables is that they are pure digital so for the most part, a cheap one will perform the same as an expensive one.