Use of the term "classical music"

The term "classical music" was not used until the early 19th century. People then started talking about classical music in order to praise the great composers such as Bach, Mozart and Beethoven. In the 20th century many different ways of composing were used, including music played by electronic instruments or very modern music using strange sounds (experimental or "avant garde" music), for example the music of John Cage. Some people feel that this kind of music cannot really be described as "classical music".

Instruments used

Classical music can be for instruments or for the voice. The symphony orchestra is the most common group of instruments for the playing of classical music. It has four families of instruments: the string instruments which include the violins, violas, cellos and double basses, the woodwind which includes flutes, oboes, clarinets and bassoons together with related instruments of different sizes, the brass instruments: trumpet, trombone, tuba and French horn, and percussion instruments which nearly always includes timpani as well as many other possible instruments which are hit or shaken. This is very different from a typical rock band which has a drummer, a guitarist, one or two singers and an electric bass and keyboard. Instruments that play classical music are not normally amplified electronically.
The same applies to the voice. Singers may be sopranos, altos, tenors or basses, depending on their vocal range. Their voices are not amplified. Opera singers, in particular, have to develop very powerful voices which will be heard over the orchestra and project right to the back of an opera house.
The instruments used in classical music developed at different times. Some of the earliest were known in Medieval music. The trombone and the triangle have hardly changed for hundreds of years, but the violin family developed from folk instruments such as fiddles and gradually replaced the viols to form the basis of the modern orchestra. This was happening by the beginning of the 17th century, which was the time when opera was invented.