What is a Planning Poker?
Planning poker is consensus-based estimation: each team member privately picks a card (usually Fibonacci — 1, 2, 3, 5, 8, 13…) sizing a story, everyone reveals simultaneously, and outliers explain their reasoning before a re-vote. Simultaneous reveal kills anchoring — nobody's estimate gets dragged by the first loud number.
The gold is in the outliers: when one person says 2 and another says 13, someone knows something. The conversation matters more than the number.
Worked example
Estimating "add export to PDF," four developers reveal: 3, 3, 5, 13. The 13 explains: the reporting service renders through a headless browser that's pinned to a deprecated version — this touches it. The re-vote lands on 8, and a risk nobody else knew about is now on the table. Averaging the first votes would have buried it.