A dollar bill can be of various kinds of currency:

• Federal Reserve dollar bill (modern U.S. currency)
• United States note (historic U.S. currency)
• Silver certificate (historic U.S. currency)
• Gold certificate (historic U.S. currency)
• Canada dollar (Canadian currency)
• Australian dollar (Australian currency)
• New Zealand dollar (New Zealand currency)

Others countries' dollars are listed at Dollar, along with the history of its use in this context, as well as other uses for the word..