0 (number)

0 (zero) is a real number and is the integer between 1 and -1, which signifies a value of nothing. It is also a numerical digit and used as a placeholder for place value systems.

History
The number zero was invented twice—once in India and once in Mesoamerica. This invention is considered especially significant, since it required a considerable cognitive leap to achieve and opened the door to a host of new applications for numbers.