A digit, commonly represented as 0, that acts as a placeholder in positional notation. The importance of zero comes not from it symbolizing nothing, but from the fact that it enables positional notation to exist at all. Before we could develop a concept of a number being represented by numerals in the ones, tens, hundreds, thousands, and so on, it was necessary to come up with a numeral that could indicate that the given number did not partake of a particular place.

It is common to refer to zero as one of the "Arabic" numbers. However, the truth is a good deal more complicated than that. The ancient Babylonians, circa 1800 BCE, used a zero (two diagonal wedges in cuneiform) as part of their system of calculation. As they were working in base 60, this is a fairly impressive feat.

Some middle Americans had a zero as early as 1000 BCE, and the Chinese were using a zero in 400 BCE.

Hindu mathematicians were familiar with the zero by roughly 500 CE. Our western zero in fact descends directly from the Hindu zero, passed on by the Arabic mathematicians. The first European to advocate the use of zero in numeric notation was Abraham ben Meir ibd Ezra (1092-1167) in his Sfer H Mispar (The Book of the Number). He called it the Sifra, from which our modern word 'cipher' derives.

Regardless of its history, the zero is arguably the most important invention in the world. Without it, we would be unable to carry out the mathematics necessary for most other fields of technical endeavour.