Credits are the standard currency in the X-universe, used by all races.
In 589, both The Foundation Guild and The Profit Guild agreed to use a common currency, called Credits. The event is known as The Great Currency Reform. The Credits remain, even today, the common currency in the X Universe.
Originally, Credits were divided into 10 pieces, with fractions of Credits denoted by a decimal. However, since the Second Xenon Conflict, prices have risen and decimal Credits are no longer used.