Bulls are speculators who believe that a market, instrument, or sector is going on an upward trajectory. This belief puts them at odds with bears, who take a pessimistic view on a market’s direction.
When trading, bulls will tend to buy (or go long on) their market, in order to make a profit by selling when it is worth more in the future. When a market is increasing in price, the bulls are seen as in control. This is referred to as a bull market; it is the opposite of a bear market, when the price is heading lower.