A melody (also called a "tune") is a series of pitches (notes) sounding in succession (one after the other), often in a rising and falling pattern. The notes of a melody are typically created using pitch systems such as scales or modes. Melodies also often contain notes from the chords used in the song. The melodies in simple folk songs and traditional songs may use only the notes of a single scale, the scale associated with the tonic note or key of a given song. For example, a folk song in the key of C (also referred to as C major) may have a melody that uses only the notes of the C major scale (the individual notes C, D, E, F, G, A, B and C; these are the "white notes" on a piano keyboard. On the other hand, Bebop-era jazz from the 1940s and contemporary music from the 20th and 21st centuries may use melodies with many chromatic notes (i.e., notes in addition to the notes of the major scale; on a piano, a chromatic scale would include all the notes on the keyboard, including the "white notes" and "black notes" and unusual scales, such as the whole tone scale (a whole tone scale in the key of C would contain the notes C, D, E, F, G and A). A low, deep musical line played by bass instruments such as double bass, electric bass or tuba is called a bassline.