This solemn word (in Latin dominus - Lord, dominantis - dominant) is called the fifth degree of the scale. This name was given because it is very important support level. It is located on the fifth (see Interval) above the primary tonic audio range and is therefore sometimes called the upper dominant. And on the fifth down from the tonic is lower dominant, usually called the subdominant.
Just called and the chords built on these steps. Dominant and subdominant agreed to designate Latin letters D and S. in Addition, they represent Roman numerals V and IV, in accordance with the stages on which they are located.