To a non informed music listener, the term 'classical music' refers to composers and compositions of the Classical and Romantic periods of western music (e.g. Beethoven or Tchaikovsky). In reality, classical music is that genre of music that is not popular music or jazz music (whatever those two may mean). Classical music includes music compositions of the western world dating from the medieval times (or even ancient times) to the 21st century excluding jazz, pop, rock and dance song cycles and music. A music history book will show you that Western music matured in the 18th and the 19th centuries but composers have used more and more the technological advancements of the 20th and 21st centuries to create a new style of classical music called some times contemporary music.