Piano
A piano is a large, musical instrument that's played with keys. Given the bulkiness and technical craft that goes into one, pianos are obviously not exactly something that can be moved around, thus piano shows tend to be special.
History
In the Pony universe, pianos are made in all sizes, so even children like Spike and Scootaloo can play pianos. However, it seems that in the Human universe, pianos are more driven for teenagers and adults. Twilight Sparkle performed on a piano during a music video she made with the rest of her friends.