Equal temperament is a musical tuning system that divides an octave into twelve equal parts, known as semitones. This allows instruments to play in any key without sounding out of tune, making it easier for musicians to switch between different keys during a performance. This system became widely adopted during the Renaissance and Baroque periods, as it provided greater flexibility for composers and performers. The most common form of equal temperament is the 12-tone equal temperament, which is used in many Western musical traditions today, including classical, jazz, and popular music.