Short interest
The number of shares sold short and not yet covered, reported by exchanges twice a month, often shown as a share of float.
Short interest is the number of shares that have been sold short and not yet bought back to cover. FINRA publishes short interest twice a month, with a settlement-date lag of several business days, so the figure is always somewhat stale. Days to cover divides short interest by average daily volume to estimate how long covering would take.
On our site, short interest is shown as shares and as a percentage of float, with days to cover. Note the report date, since the data is delayed.
Traders care because high short interest can make a stock vulnerable to a squeeze if prices rise and shorts must cover. It can also reflect a well-founded bearish view.
Worked example (illustrative numbers, not real data): a stock has 10 million shares sold short, a float of 50 million and average daily volume of 2 million. Short interest is 20 percent of float and days to cover is 5. A rally could force covering over several sessions.