2. After each movement of a multi-movement work. Major works, such as symphonies and concertos, typically consist of multiple separate sections called "movements." It is customary to applaud between each movement, although if the movements follow directly, clapping can be held off until the end.
3. At the end of the entire piece. After the last note has been played, the audience generally gives a hearty and enthusiastic round of applause for the entire performance.
4. Following a particularly virtuosic or expressive performance. If an orchestra member or conductor performs a particularly impressive passage or phrase, it is common for the audience to express its appreciation with a spontaneous burst of applause.
It is important to remember that these are just general guidelines, and applauding at a concert is ultimately up to the individual concertgoer. However, by following these guidelines, you can ensure that you are being courteous to the performers and fellow audience members.