Encores are not usually rehearsed and are often chosen spontaneously by the performers, based on the audience's reaction or requests. They can consist of a popular or well-received song from the main set, a cover version of a different artist's song, or even an improvised performance.
The tradition of giving encores dates back several centuries and is associated with the concept of "adding something extra" to show gratitude to the audience and extend the enjoyment of the performance. In classical music concerts, encores are generally expected and serve as a way for performers to express their appreciation and connect more closely with the audience.
In contemporary popular music concerts and performances, encores may or may not be part of the planned program, but they are often given in response to enthusiastic crowd reactions. Some performers or bands have signature encore songs that are regularly requested by fans.