The rate of exchange between currencies can be managed in a variety of ways:
Single currency peg - one country's currency is linked to that of another country, with little opportunity for adjustment.
Composite currency peg - one country's currency is linked to a basket of currencies of its major trading partners. Often a weighted average is used.
Managed float - this is effectively a single currency peg with more frequent adjustments to the rate permitted.
Independent float - rates of exchange are determined only by market forces.