Lets start with the word itself. Here's how wikipedia defines karaoke. Many of us ozzies mispronounce the word and as a result, end up spelling it like it was an english word "karEoke". Whoops, we do it all the time. So, the correct word is of course "karaoke" which is a portmanteau (blend of two words, in this case Japanese) of "KARA" translates to "empty" and "OKESUTORA" translates to "orchestra". So, Kara Oke - Empty Orchestra. For correct prounciation try to say the words separately with a Japanese accent.
Well, these days, karaoke is the experience of singing along with some pre-recorded music (minus the lead vocals) and reading the lyrics off a screen. I'm amazed at how many people still ask "Do the words come up on the screen?" Well yes they do!
Karaoke is a form of entertainment often offered at pubs and clubs but can be held at private functions and of course at home. There is no upper age limit to singing, so you adults who have children on the sing star. Its not just a toy for kids. In fact the old sing star has a pretty good karaoke functionality that any adult could practice with, so next time you send them to their room, sneak a song or two in.
Keen karaoke singers often have some of their own karaoke discs which they practice with at home and then take to a venue for a larger experience.