Numbers with multiple digits are separated by commas into groups of three called periods. From right to left, each period contains a place for ones, tens and hundreds.
Starting from the right, the most commonly used periods are called ones, thousands, millions, billions and trillions. Other names for a group of three include trio, derived from Italian, and triad. Three months is called a trimester, and a triennium measures three years. A triplet describes three usually identical items, and triple describes three ordered elements. Triumvirate is a quantity of three, and it’s derived from the Latin word “trium virum,” meaning of three men.