The double bass is a big stringed instrument that terms, perhaps more correct, include contrabass and upright bass. It is used in orchestras, jazz bands, rockabilly bands, bluegrass music, and some country music bands. It plays low-pitched musical notes in musical ensembles and bands. In jazz bands, these low-pitched musical notes are called the "bass line." The double bass looks like smaller instruments like the violin, viola, and cello.