As

As (sign: £; plural: assi) is the primary monetary unit of Panem and thus, the primary currency of the Capitol. Notably, as is used as the primary currency for the Kill Credits. The money won by a Tribute is generally sent to them in envelopes after the end of each Arena, if they'd scored killings. Whether the money is in coinage or in bills is currently unknown.

In real world terms, 1£ is equivalent to $5USD. Thus, one kill in the Arena would fetch a Tribute $500USD.

Trivia

 * In real life, the As was the rough equivalent to the American dollar during the Roman Republic and part of the Roman Empire. It was also known as libra due to its equivalent usage in weights and measures. An as/libra was thus also a pound in weight (albeit a Roman pound, which was roughly equal to the weight a regular can of soda). The as was eventually phased out in favor of a system where the base coinage was a denarius (which, originally, was the equivalent of 10 asses). However, the name libra lives on, adapted by future civilizations, first as the currency libra, and then, lira.