A concert is a live performance, usually music, before a small or large audience depending on the size of the venue held and the popularity of the musician(s) performing. The music may be a recital of one musician or a musical ensemble such as a band, orchestra or choir. The atmosphere varies depending on the type of concert and the music being played. For example, a classical or jazz concert is generally rather downtempo with the audience seated. A rock concert, however, is usually quite different with the audience standing, and quite possibly dancing, singing, screaming, jumping around, waving their arms around or even headbanging etc.. Depending on the type of music. That's a very basic outline, there are many videos of concerts on the internet which will give you a good idea of what they are and the atmosphere.
Hope I was helpful in some way.
