音程(interval)
指音乐上两个听起来具关联性的音，尤其指它们在音乐空间中的距离。在西方音乐中，音程通常依音域中所涉及的调（key）的数量而命名，因此，自C攀升至G（C-D-E-F-G）即为5度，因为音程中有5个音域程度（必须包括头尾两个音）。而C-E-G和弦（chord）则是由两个音程所形成，即C到G的5度和C到E的3度。一个音程除了可以简单的数字表示以外，它还有更精确的名称，例如C-E即为一个大3度（因为它包括了4个半音〔semitone〕），C升E则为一个小3度（具2个半音），C-E降半音亦为一个小3度（具3个半音），C-E升半音是一个增大的3度（具5个半音），C升半音E降半音则为减小的3度（有2个半音）。3度和6度音程被归为3度音程之列，而第4和第5音程则属於完全音程（一个完全4度音程包括5个半音，而完全5度音程则有7个半音），增大则是由一个半音所扩增，同理减小亦为由一个半音所缩减。
English version：
interval
In music, two tones heard in relation to one other, and specifically their distance in musical space. In Western music, intervals are generally named according to the number of scale-steps within a given key that they embrace; thus, the ascent from C to G (C-D-E-F-G) is called a 5th since the interval embraces five scale degrees (inclusive of those at both ends). The chord C-E-G is made up of two intervals, the 5th C-G and the 3rd C-E. An interval with a simple numerical designation will also have a more precise name; thus, C-E is a major 3rd (since it consists of four semitones), C-sharp-E is a minor 3rd (three semitones), C-E-flat is also a minor 3rd (three semitones), C-E-sharp is an augmented 3rd (five semitones), and C-sharp-E-flat is a diminished 3rd (two semitones). 2nds and 6ths are classified like 3rds, whereas 4ths and 5ths are classified instead as perfect (a perfect 4th consisting of five semitones, a perfect 5th of seven semitones), augmented (when expanded by a semitone), or diminished (when contracted by a semitone).