Zero

Zero, or 0, is the name traditionally given to the additive identity in number systems.

The development of a concept and notation for 0, probably in ancient Indian civilization, and its subsequent transmission to Europe via the Persians and Arabs, was fundamental to the success of western mathematics in fields beyond geometry. It has suprisingly much relevance due to its significance in positional number systems. For instance, normal commercial interactions might be seriously slowed if cashiers had to make change on a purchase of $LXIV with bills marked $L, $X, $V and $I when handed $XC.