Wait a minute! I know what classical music is. Its music from hundreds of years ago played by big orchestras with lots of violins and a old guy in a black suit waving a stick leading the whole show. Right? Wrong!
Well, partially right. Classical music can be like this, but it encompasses a whole lot more. Classical music includes Gregorian chant from a thousand years ago, but also the music of Philip Glass from just last month. It can be as simple as a single singer performing a song, a group of friends playing a string quartet, or an orchestra with hundreds of players. It can be background music, or it can wake you up and make you listen.
So what IS classical music?
Classical music is not so much from a particular time, as written for a particular reason. It is the art music of the Western World. If popular music is written to simply entertain, then classical music is written to express something significant or great. It is written to express an idea, explore a theme or let loose an emotion. Most importantly, it aims to transfer that idea or theme or emotion to the listener, and make them THINK.
This is not to say that classical music is any better than popular music. Their purposes are different. Popular music aims mainly to entertain and can do that sometimes better than classical music, but classical music has a deeper level.
Remember that even during the times of Mozart and Beethoven, classical music was not popular in the sense that it was enjoyed by the masses. Only the wealthy classes who had the time and resources were exposed to classical music, while the general population made do with songs and bands that formed the popular music of their time. It is unfortunate that this elite divide persists today. Classical music is for everyone!
The same way that pictorial art is not always beautiful, so classical music can be dark, or dissonant, or difficult. Sometimes a piece of classical music is instantly attractive. Other pieces may take several listenings to appreciate what the composer is trying to say.