1) A period of music ranging from the middle 1700s to the early 1800s. Famous classical composers include Beethoven, Mozart, and Haydn.
2) A bastardization of all "traditional" types of music (orchestral, choral, etc.). Derived from the classical period. Other periods include prehistoric, medieval, renaissance, baroque, romantic, 20th century, and 21st century.
3) The true pinnacle of music in which true musicianship, expressiveness, technique, and skill are essential elements in its performance. To truly listen to classical music one must be able to listen to it on entirely different levels of thinking.
The only classical music that most people have listened to is the ambient, therapeutically-designed background music at Barnes & Noble.