A mathematical measurement of the degree of uncertainty of a random variable. Entropy in this sense is essentially a measure of randomness. It is typically used by financial analysts and market technicians to determine the chances of a specific type of behavior by a security or market.

Entropy has long been a source of study and debate by market analysts and traders. It is used in quantitative analysis, and can help predict the probability that a security will move in a certain direction or according to a certain pattern. Volatile securities have greater entropy than stable ones that remain relatively constant in price. The concept of entropy is explored in "A Random Walk Down Wall Street."