Core terms
Fat-finger error
An order-entry mistake such as a wrong share count, side, price or symbol. An order sent by mistake that fills at normal market prices generally stands.
Common forms are a neighbouring hotkey that doubles the size, a sell sent instead of a buy, an extra digit in the price, or an order sent while the window still shows the previous symbol. Hotkeys speed up mistaken orders as much as correct ones. In an Illustrative example, a doubled 1,200-share order that hit its stop lost −1.92R against a planned −1R loss.
Clearly erroneous transactions
FINRA Rule 11890 describes a clearly erroneous transaction as one with an obvious error in a term such as price, number of shares or the identification of the security. In practice, reviews of trades in exchange-listed stocks apply numerical guidelines based on how far the trade price was from a reference price, under FINRA's rules for over-the-counter trades and parallel exchange rules (as of 2026-10-05). A mistake that filled near the market usually does not qualify, so the position and its result stay with the trader.
What traders should verify
Build safeguards into each key (share and position-value caps, a buying-power fraction, checks for a stop on the wrong side) and log every mis-keyed order, including those a safeguard rejected, with its cause. Some traders count a mis-keyed loss against their daily loss limit so one error cannot cascade.
Do not conflate
Trader usage; there is no official definition. Whether a trade can be broken is decided by the venue or FINRA under the clearly erroneous rules, based on the trade's terms rather than the sender's intent; plan on the assumption that an error fill stays.
Primary source
Primary sourceFINRA Rule 11890, Clearly Erroneous Transactions