a series of notes with tones that are low in pitch or frequency

A bassline (also spelled bass line) is the term used in many styles of popular music, jazz, and blues, and funk for the low-pitched instrumental part or line played by a rhythm section instrument such as the electric bass, double bass, or keyboard (piano, Hammond organ, electric organ, or synthesizer). Basslines are in the bass, which means that they are lower in pitch than the other musical parts (chords, instrumental melodies, and vocal melodies).