A fixed exchange rate is a rate which is maintained
and controlled by the central government. Under this system, the value of
currency is fixed against different currencies to ensure stability in exchange
rate and promote foreign trade.
A Flexible exchange rate is a rate which is
determined by the market force. It is controlled by demand and supply forces,
which is why it is called as free rate of exchange. There is a minimum or no
government intervention, and the government does not hold any reserves. There
is no problem of overvaluation or undervaluation of currency.