It's a whole series of evenings where mostly classical music is played by a huge orchestra, but they have various interludes where famous musicians will come and play solo performances bringing a completely different slant to the event.
It's all done in a lighthearted way to bring Classical Music to the masses, so kids get involved and frequently the audience all get involved.
It became such a success that the BBC started covering it so now millions watch it.
If you're into it, it's great fun.
PPB isn't into it. At all.