A subjective measure of how investors are feeling about a security or market. Generally speaking, market sentiments are positive when stock prices are going up and negative when they are going down. Because feelings sometimes change more slowly than a market's underlying fundamentals, market sentiment helps explain why securities have a tendency to become either overvalued or undervalued. Some investors plan to make investment decisions in a way that disregards market sentiment, while others attempt to profit from it. See also: Crowd theory, Subjective probabilities, The Theory of Moral Sentiments.