It is a place (usually a bar or restaurant) where people can get up to sing publicly. There is a machine that plays the music without the lyrics, from popular songs, and the patron can read the lyrics off a teleprompter and sing along. It is that person’s chance to perform in public. I have never been to something like that, but I have seen it in the media. I have never heard of a Jewish Karaoke place though, and certainly if there is one, it is unlikely to be for frum people, I would imagine.