If it gets your signal in or out, it's probably here.
Talking about connections isn't very exciting. Cables themselves are about as sexy as hair clippings. Both are crucial, though, in getting the best-quality signal from your source components to your playback components. (This doesn't include hair clippings). So, here is a list of all the connections you're likely to come across and how they do what they do. They're also arranged in order from worst to best. Keep in mind that, in some cases, the connector and the signal share the same name; in others, the connector isn't exclusively associated with a particular type of signal.