The term 'written in a specified key' refers to a piece of music that has been composed or arranged in a particular key. This means that the notes and chords used in the piece are all within the same key signature, which is a set of sharps or flats at the beginning of the staff that indicate which notes should be raised or lowered in pitch. The crossword solution for this term is 'tonal, ' which means that the piece of music is based on a tonal center, or a single note or chord that serves as the basis for the entire composition. Tonality is an important element of music theory, and it is often used to create a sense of unity and structure in a piece of music.