If someone is considered to be bearish, the stock market is heading down. Bearish trend in the market means, the prices of stocks of companies are falling down. And if the stock prices of companies are going up, the market is said to be bullish.
People usually tend to buy the stocks when they think that market is going to be bullish. It means there would be an upward trend of the stocks. Similarly, people don't buy stocks when they think that market is going to be bearish, means there would be a falling trend in the stock market.