What does the instruction 'tre corde' indicate to a pianist?

The instruction 'tre corde' translates from Italian to 'three strings' and indicates to the pianist that they should release the una corda pedal, which softens the tone by allowing the hammer to strike only one string instead of three. When 'tre corde' is written in the music, it signals the performer to return to the full sound of the piano, utilizing all three strings for each note instead of just one. This instruction is important for achieving a richer timbre and dynamic contrast in the performance.

The other options do not accurately represent what 'tre corde' signifies. For instance, pressing the left or soft pedal (the una corda) goes against the instruction, as does playing softly, which is contrary to the intended full sound that 'tre corde' invokes. Holding the note longer does not pertain to the 'tre corde' marking and is unrelated to the pedal instruction. Understanding this term helps pianists make appropriate interpretive choices in their playing.