Financial markets are markets for financial (as oppose to real) assets and liabilities. Although there are many ways to classify financial markets, a market's most important characteristic is its liquidity. Liquidity refers to the ease with which you can capture an asset's value. Liquid assets can be quickly converted into their cash value. Liquidity is closely related to transaction volume, with high-volume markets being more liquid than low-volume markets. The interbank currency and Eurocurrency markets enjoy high liquidity in large part because of the high volume of trade.
Another dimension along which financial markets vary is according to maturity.