Market sentiment is the feeling or attitude of investors about how the stock market will perform. When people talk about sentiment, they are talking about the general feeling that the market is either going up or down.
When investors are feeling confident, they are more likely to buy stocks and invest in them. This causes stock prices to go up, and this is called a 'bull market'. When investors are feeling worried, they are less likely to buy stocks and, instead, will look to sell them. This causes stock prices to go down, and this is called a 'bear market'.
Market sentiment is important because it helps investors decide when to buy and sell stocks. When investors think that the market is going to rise, they will buy stocks. When they think it is going to go down, they will sell. That way, they can make money from buying low and selling high.