Classical music is a broad term that usually refers to music produced in, or rooted in the tradition of Western art, Christian music, and orchestral music, covering the period from about the 9th century to the 21st century. European classical music is distinguished from non-European forms of music and popular music largely by musical notation system, which has been used since around the 16th century. Western music notation used by composers to give instructions to the carrier music on the pitch, speed, metrum, individual rhythms and exact nature of a piece of music. This limits the existence of practices such as improvisation and ad libitum ornamentation is often heard on non-European music (compare Indian classical music and Japanese traditional music) and popular music.