FINRA publishes daily data on U.S. stock trades that happen away from the public exchanges (NYSE, Nasdaq) — mostly through large trading firms called market makers (e.g. Citadel Securities, Virtu) that fill orders placed through everyday retail brokerage apps.

“Short volume” here doesn’t necessarily mean someone is betting a stock will fall. When you place a buy order, it’s often routed to one of these market makers, who fills it out of their own inventory. If they don’t have the shares on hand, they sell them to you short — borrowing shares to sell now and buying them back later. So a spike in short volume can actually reflect a lot of people buying, not selling.

This is a rough signal, not a certain one. It shows a day’s trading flow, not whether the market maker is still short by the close — and on options-heavy stocks, some of this volume comes from market makers hedging, unrelated to retail buying or selling.

Bottom line: a high “% short” often points to heavy off-exchange trading interest — more often tied to buying than selling — not necessarily bearish sentiment.