"Bulls make money, bears make money, pigs get slaughtered" is an old investment industry saying that warns against being excessively greedy. Since pigs typically eat a lot, the term "pigs get slaughtered" is a metaphor that describes those who assume too much risk in an attempt to quickly generate large short-term returns.

The bulls and bears in this expression take views on the market's outlook but not excessive risk. If the stock market is trending up, it's considered a bull market. If the market is trending down, it's considered a bear market.

Keep reading to learn more about bulls, bears, and pigs -- as they pertain to the stock market anyway.

A digital board displaying stock prices in green and red.

Image source: Getty Images.

Bulls

A bull market is occurring when stock prices are generally trending upward. These periods are marked by investor optimism and confidence. During bull markets, the economy is usually healthy, unemployment is low or trending lower, consumer spending is rising, and average enterprise sales and profits are rising. Bullish investors believe the upward trend will persist for the foreseeable future and thus tend to keep purchasing more stocks. The combination of a healthy economy, business growth, and investor confidence creates a cycle in which stocks gain value over time -- sometimes for many years.

The bull as a symbol is derived from the manner in which the animal attacks. A bull tends to charge with its horns thrusting upward into the air.

Bears

A bear market is one in which pessimism and low investor confidence reigns. Bear markets tend to coincide with economic recessions, high unemployment, low or declining consumer spending, and weak corporate sales and profits. Holding a pessimistic outlook on the economy, bearish investors are likely to sell stocks, causing stock prices to fall. Investing during a bear market can be profitable but also challenging because it's hard to determine which businesses will perform better than their peers. When a bear market ends is hard to predict.

The bear is symbolically derived from the manner in which bears attack. Bears tend to swipe their paws in a downward motion.

Pigs

Pigs are investors who assume high degrees of risk, or overlook risk entirely, with a singular focus on short-term profit. They make rash investment decisions or buy stocks without conducting enough or any research. As a result, pigs tend to lose money and potentially a lot of it -- hence the adage they get "slaughtered."

Bulls and bears have opposite investing styles, but each type of investor can make money over the long-term by investing according to their stated investment goals and strategy. Pigs, by contrast, eschew long-term goals and approach investing inconsistently.

The phrase, "Bulls make money, bears make money, pigs get slaughtered," is also the title of a 2002 book by Anthony M. Gallea containing general investing tips and advice.