Core terms
Short interest
The number of a stock's shares that have been sold short and not yet covered, as reported by brokers on set dates. It is published about twice a month, so it describes positions with a delay.
FINRA Rule 4560 requires member firms to report short positions in customer and proprietary accounts twice a month, and FINRA publishes the totals after each settlement date. Data sites often express short interest as a percentage of float ("short float"), which inherits the float estimate's problems.
Short interest is a stock of open positions. Short volume is a flow: the share of a day's trading volume marked as short sales, which includes market makers' routine short sales and says little about lasting bets against a stock.
What traders should verify
Note the settlement date the figure refers to. In a fast-moving small cap, a two-week-old short interest number may not describe today's positions.
Do not conflate
Do not mix short interest with daily short volume. A high short interest does not by itself cause a squeeze.