Planning Poker | Scrum/Agile user story estimating

From the website:

Planning Poker is a consensus-based estimating technique. Agile teams around the world use Planning Poker to estimate their product backlogs. Planning Poker can be used with story points, ideal days, or any other estimating unit.

The product owner or customer reads an agile user story or describes a feature ... Each estimator is holding a deck of Planning Poker cards with values like 0, 1, 2, 3, 5, 8, etc. ... estimators discuss the feature, asking questions ... When the feature has been fully discussed, each estimator privately selects one card to represent their estimate ... All cards are revealed at the same time.

Please see the website for many more details.