What is "tasto solo"

Tasto \Tas"to\ (t[aum]s"t[-o]), n. [It.] (Mus.) A key or thing touched to produce a tone.

Tasto solo, single touch; -- in old music, a direction denoting that the notes in the bass over or under which it is written should be performed alone, or with no other chords than unisons and octaves.

Tasto solo is an Italian term used in music scores, usually on the continuo part, to indicate that a note or section should be played on its own, without harmony. The term tasto is Italian for fingerboard, so the part is to be played solo by the fingerboard instrument (e.g. cello) and not by the harmony instrument (e.g. harpsichord) where a basso continuo line is played by more than one instrument. The phrase first appeared in music theory books in the eighteenth century, but was used by composers such as Arcangelo Corelli before this time. C.P.E. Bach commented that, in practice, Italians did not play tasto solo.