Definition
Planning Poker is a consensus based Agile estimating and planning technique. A session usually starts when a the product owner or customer, reads an agile user story/describes its features to estimators. Each estimator holds a deck of Planning Poker cards with numerical values, that represent story points, ideal days or other units.
The feature is then discussed by the estimators, and questions are asked of the product owner as needed. After the complete discussion regarding the feature, each estimator privately selects one card to represent his/her estimate. After which, all cards are then revealed at once.
If all estimators selected the same value, it becomes the official estimate. If not, the estimate is discussed again among the estimators. The high and low estimators share their reasons, and after further discussion, each estimator reelects a card. All cards then, are revealed again at the same time.
The process is repeated till a consensus is achieved or till the estimators defer it till further information is revealed.
Further Reading