Binary means composed of two parts and comes from the Latin, originally meaning "two by two". The idea is that a whole is in one of two possible conditions and no other condition is possible. Specifically, the whole is in condition 1 or the whole is in condition 2. For example, the switch is on or the switch is off, the page has data on it or the page is blank. Applied to a numbering system, a place holder has no data, represented with the symbol, 0 or the place holder has data present, represented as 1. There are no other conditions in a binary system. Electronics commonly use 0 to mean "no voltage is present" 1 to mean "a voltage is present".