HDMI stands for "High-Definition Multimedia Interface". These days, if you want absolute quality audio/video from your source, HDMI is the way to go.

HD, or "High-Definition" is fast becoming a popular buzzword, as more and more shows crop up on cable in HD and movies get released on the Blu-Ray format. It's one of the luxuries of the digital age that pretty soon, will become ubiquitous I'm sure.

If you already know why, feel free to skip this bit.

An HDMI splitter basically splits one HDMI source signal into multiple outputs. Typically, you have 1x2 HDMI splitters, though 1x4 or even 1x8 are not uncommon.

Tired of having to disconnect and reconnect your HDMI cable from one TV to another? If you have multiple TVs, or a TV and projector you frequently use, a splitter would get rid of this problem.

You could either leave both TVs on (for whatever reason) and they'll both show the same thing synchronized. Or you could just use any one of them individually when you feel like it. The splitter doesn't need both of them plugged in to function.

Or maybe you have a TV and a home theater system set up, but don't necessarily want to use the home theater system for every single viewing. You could hook up the splitter to both of them, and just turn on the home theater system when needed.

Powered HDMI splitters are generally larger and more well-constructed. They also usually cost more.

Simple HDMI splitters are smaller and cheaper.

Which one to go for? It depends a lot on your setup, which we'll get into a bit later. You could get things working fine with a simple HDMI splitter and some decent quality cables, provided the cables you're using are no longer than 5 meters. Generally though, it's a good idea to go with a powered HDMI splitter.

As with anything tech-related, whether things actually work or not depend on your setup.

HDMI Splitter. As I've mentioned earlier, a powered splitter would be best in general. If you're in any doubt about whether the splitter you're looking to purchase is any good, do look around for any reviews, or make a post in a forum asking about it. Do also keep in mind that results may vary from setup to setup, so just because a splitter works wonderfully in one, doesn't mean it will do the same for your own setup.

HDMI Cables. Best to get good quality cables if possible. You could possibly get away with poor quality cables shorter than 5 meters, but beyond that, go premium. Keep within 10 meters at the most. If for some reason, you really need cables that stretch even further, then expect to invest in an HDMI booster/extender.

Source. This could be your cable box, Blu-Ray disc player, PC, PS3 or Xbox 360. If the source sends a strong enough signal, then you could use either poorer quality cables, or longer ones.

Output. If your output has a high enough sensitivity, then again, you could use either poorer quality cables, or longer ones.

If you experience any problems such as no video/audio showing on your output, the easiest solution would be to get a better quality cable, or shorten the distance between your output and the splitter. Don't worry if you're using cables of differing length for each of your outputs. The video/audio on them will still be in sync.

• Wikipedia - HDMI
  
• HDMI Specification Official Site
• High Def Forum - Cables & Connections