Meaning of "classic"

The word “classic” tends to mean: an art which is so good that it will always be enjoyed by future generations. It is something that has become a model for future artists. The period of Ancient Greece and Rome is known as the Classical Period because, many centuries later, people looked back to those ancient civilizations and thought they were perfect. In recent European history the 18th century was known as the Classical Period because musicians, artists, writers and philosophers were inspired by the art forms of the Classical Period of Ancient Greece and Rome. Something that is a “classic” is therefore something that will always be remembered as something great. Famous books such as the novels of Charles Dickens are called "classics". “Classical music” therefore tends to mean music that will not be forgotten soon after it is written, but is likely to be enjoyed by many future generations.

Contrast with pop music and jazz
Although people sometimes think of classical music as the opposite of pop music, it can still be very popular. Like all kinds of music, classical music can be in many different moods: happy, sad, scary, peaceful, thoughtful, simple etc. Mozart wrote his serenades and divertimentos to entertain people at parties. Classical pieces of music can be quite short, but they can also be very long, like a big, musical story. A symphony by Mahler or Shostakovich can last for nearly an hour, and an opera is a whole evening’s entertainment.

Classical music is also different from jazz because true jazz is improvised. However, the differences are not always obvious. Classical music has often been inspired by jazz, and jazz by classical music. George Gershwin wrote music which is both jazz and classical. Classical music, too, can be improvised. The great composers Bach, Mozart and Beethoven often improvised long pieces of music on the organ, harpsichord or piano. Sometimes they wrote these improvistions down. They were, in effect, compositions which were composed in one go.