"Sinfonia" is just Italian for "symphony" and originally comes from the Greek symphonia meaning "agreement or concord of sound". In the 17th century and for most of the Baroque period, the terms symphony and sinfonia were used for a range of different compositions, including instrumental pieces used in operas, sonatas, and concertos – usually part of a larger work. The opera sinfonia, or Italian overture had, by the 18th century, a standard structure of three contrasting movements: fast, slow, fast, and dance-like. It is this form that is often considered as the direct forerunner of the orchestral symphony. The terms "overture", "symphony", and "sinfonia" were widely regarded as interchangeable for much of the 18th century.