Depends on how the microphones are placed. Obviously, if there is only one microphone the recording is Mono, even though the live performance could be heard in stereo if the band is divided more or less evenly across the stage and you are sitting dead-center in the audience. It is recorded in Stereo when there are two or more microphones placed to record the right and left side of the stage performance separately. Those two separate channels can have some overlapping music and still be Stereo. Many Mono recordings were actually recorded in Stereo and mixed to Mono, or "folded-down" to Mono. So a Live Concert can be both Mono and Stereo to the audience depending on where you are sitting and whether you are listening to the live sound of the actual performers or to the performance as broadcast over the amplification system used in the concert hall.