Ternary numeral system

A ternary /ˈtɜːrnəri/ numeral system (also called base 3) has three as its base. This means that you can only count with 0, 1, and 2. The first ten numbers in ternary are 00, 01, 02, 10, 11, 12, 20, 21, 22, 100. When all the digits in the number reach 2, you add a 1 in front and change everything else to 0. There is another system with the same name more specifically called the balanced ternary system. This system is called that way because 0 is the middle digit, with the other two digits being -1 and 1. That system is used in comparison logic and ternary computers. 
Similar to a bit in binary, a ternary digit is called a trit.