A typical noraebang. The 방 character on the right is fashioned to look like a musical note, with the two notes on the upper left representing a ㅂ, and the note on the right both the ㅏ on the right and the ㅇ below.
A noraebang (노래방, song.room) is an area people pay to go to to sing songs in a private room. The concept is exactly the same as karaoke rooms in Japan and within the rooms is a phone where one can order food and drinks. Each room has a number of microphones and song books; one picks a song to sing by inputing the number.
Not all 노래방 machines are equal. There are two major manufacturers of 노래방 machines in Korea, 금영 'KumYoung' and TJ 'TaiJin'. You can see the new songs for that week or month usually posted outside the entrace to 노래방s around the country. Some 노래방s have both machines, to cater for those who have a preference, but most will only have one of either. As a rule of thumb, TJ machines have a wider variety of popular Western songs available than 금영 machines.
It should be noted that noraebangs don't provide prostitution, per se, but most can facilitate it. You may notice cars whizzing through streets at night, dropping off and picking up girls in front of the odd noraebang. That's often because 'singing girls' can be called up and order to your room for singing companionship. These girls are not necessarily prostitutes and many noraebangs may not appreciate any frolicking in their rooms, but arrangements with the girls have been known to be made.