Classical music is a broad term that usually refers to mainstream music produced in, or rooted in the traditions of Western liturgical and secular music, encompassing a broad period from roughly the 9th century to present times. The central norms of this tradition became codified between 1550 and 1900, which is known as the common practice period. European music is largely distinguished from many other non-European and popular musical forms by its system of staff notation, in use since about the 16th century.Western staff notation is used by composers to prescribe to the performer the pitch, speed, meter, individual rhythms and exact execution of a piece of music. This leaves less room for practices, such as improvisation and ad libitum ornamentation, that are frequently heard in non-European art music (compare Indian classical music and Japanese traditional music) and popular music. The public taste for and appreciation of formal music of this type waned in the late 1900s in the United States and United Kingdom in particular. Certainly this period has seen classical music falling well behind the immense commercial success of popular music, in the opinion of some[who?], although the number of CDs sold is not indicative of the popularity of classical music. The term “classical music” did not appear until the early 19th century, in an attempt to “canonize” the period from Johann Sebastian Bach to Beethoven as a golden age. The earliest reference to “classical music” recorded by the Oxford English Dictionary is from about 1836. Many writers feel that “classical” is an inappropriate term for mainstream and avant-garde music written since the latter part of the 19th century; hence the common usage of scare quotes .

Classical and popular music are often distinguished by their choice of instruments. There are few if any genres in which so many different instruments are used simultaneously by performing groups such as symphony orchestras, which often contain as many as 5 or so different types of string instruments including violins, violas, cellos, double basses and harp; 7 or more types of woodwind instruments; 4 or so types of brass instrument; and many diverse percussion instruments, sometimes as many as 10 different types. Also prevalent, especially in opera, is the human voice. Comparatively, most popular music genres involve fewer instruments. For instance a typical rock band will consist of a drummer, a guitarist or two, a singer or two, an electric bassist and, less universally, a keyboardist; Of course, crossover influences, such as string sections in pop recordings, are very popular as well, but rarely are backing strings considered to be part of pop or rock bands.

The instruments used in common practice classical music were mostly invented before the mid-19th century (often much earlier), and codified in the 18th and 19th centuries. They consist of the instruments found in an orchestra, together with a few other solo instruments (such as the piano, harpsichord, and organ).Electric instruments such as the electric guitar appear occasionally in the classical music of the 20th and 21st centuries. Both classical and popular musicians have experimented in recent decades with electronic instruments such as the synthesizer, electric and digital techniques such as the use of sampled or computer-generated sounds, and the sounds of instruments from other cultures such as the gamelan.

None of the bass instruments existed until the Renaissance. In Medieval music, instruments are divided in two categories: loud instruments for use outdoors or in church, and quieter instruments for indoor use. Many instruments which are associated today with popular music used to have important roles in early classical music, such as bagpipes, vihuelas, hurdy-gurdies and some woodwind instruments. On the other hand, the acoustic guitar, for example, which used to be associated mainly with popular music, has gained prominence in classical music through the 19th and 20th centuries.