Short interest is a number that shows how many stocks in a particular company have been sold, but not yet covered by buyers in the same market. It is an important number for investors, because it reveals the level of bearish (when the number of shorts increases) or bullish (when the number of shorts decreases) sentiment among institutional investors, investment banks, hedge funds, and other large, sophisticated investors.

One way to get a clearer picture of short interest is to compare it to the total number of shares that are publicly available to be bought or sold. This will give you a short interest ratio, which is the percentage of the total number of shares that have already been sold short but not yet covered. For example, a short interest ratio of 10 percent means that 10 percent of the shares available to be bought or sold are currently held by people who are betting that the share price will fall.

An increase in short interest may indicate that investors are becoming more bearish on a company's future, while a decrease in short interest could mean that investors are becoming more optimistic about the company's outlook. It is important to note, however, that investors can be wrong. For example, an increase in short interest in a company's stock could simply mean that investors are taking a defensive stance to protect themselves against possible losses, not necessarily that they are actually bearish on the company’s outlook.

Short interest can be useful for investors who are looking for trading opportunities. For example, if the short interest ratio for a company is high, this could signal a potential opportunity to short the stock and benefit from a potential drop in the price. Conversely, a low short interest ratio could signal a potential opportunity to buy the stock, as investors might be expecting it to rise.

In summary, short interest is a measure used by investors to gauge the bearish or bullish sentiment of the market for a particular stock or even the overall market. It is an important number for traders, as it can signal potential opportunities to capitalize on market moves.