Why it matters
Partial fills create unintended exposure and can break risk plans.
Trading use: the point is not vocabulary. The point is prediction: what changes when this shows up?
Common trap
Assuming a single fill or assuming unfilled size is cancelled automatically.
Example
You exit 10 lots; only 6 fill; you remain exposed on 4.
Operational cue: if you can’t point to it on the chart, in the DOM, or in your broker logs, treat it as a story and trade smaller.
Notes
Always verify filled quantity and remaining exposure.
Quick rule
- If you see this repeatedly, you are in a different regime than your model assumes.
- Regime change usually means position size change.
- When in doubt: trade smaller, or don’t trade.