If buying or trading long is the result of the trader's belief that a cryptocurrency rate will go up, then this sentiment is called being bullish. When a trader says "I'm bullish on BTC," it means that he or she believes that its rate will continue climbing. Being bullish or being a bull can mean both a belief and an action on the part of the trader. One can have bullish beliefs but actually sell (go short) assets they're bullish about, depending on the market situation and their circumstances.
The term "bull" or "bullish" originates from the bull, who strikes upwards with its horns, i.e. driving the rates up. Bullish, bull, and long are often used interchangeably. A crypto trader may say "I am long" or "I am a bull."
Being bearish is the opposite belief/action system. It means that the trader thinks that the price of a digital asset will fall. A bearish trader may choose to take an action on their market sentiment or not. If they do act, they may sell the crypto assets they own, i.e. "go short."
The term "bear" or "bearish" originates from the bear, who strikes downward with its paws, i.e. pushing the rates down. Bearish, bear, and short are often used interchangeably. A crypto trader may say "I am short" or "I am a bear."
Bearish or bullish (or long and short) trades should only be undertaken based on well thought-out and thoroughly tested trading strategies.