What it is:
How it works (Example):
Since U.S. currency notes were first introduced in the early 1800s, their color has customarily been green. For several decades until the end of the American Civil War, the U.S. federal government was unable to fully back currency notes, and most banking authorities were unwilling to fully honor their face value. As a result, the term "greenback" began as a derogatory term that over time, evolved into common slang. Once dollar bill denominations were centrally issued and universally acceptable as a form of payment, other vernacular terms including "buck" were introduced into common language.