action The mechanism by which the movement of fingers on a keyboard instrument are translated into the plucking or striking of a string (on a harpsichord [89.4.2363; 89.4.2929; 89.4.1220], clavichord [1986.239], or piano [89.4.1219]), or the sounding of an organ pipe. 

basso continuo The characteristic form of instrumental accompaniment during the Baroque period, ca. 1600–1750. The melodic bass line would often include numerical shorthand indicating what chords to play, which the player would improvise on keyboard, some sort of lute (1988.87), or harp. The chordal player (or players) was sometimes joined by a bass viol (1990.223; 89.4.1343), cello, bassoon, or violone playing the bass melody. The exact composition of a continuo section and the style of chords was rarely specified, but rather left to the performers to devise according to local tradition and the character and context of the piece.

Very complicated answer ! Are you a music teacher or something ?