According to the PMBOK Guide, planning poker is a technique used to estimate the size of user stories in agile projects. It involves each team member privately selecting a card with a number that represents the relative size or complexity of a user story, and then revealing their choices simultaneously. The team then discusses the reasons for the differences and repeats the process until they reach a consensus or an acceptable range. This technique helps the team to avoid anchoring, groupthink, and estimation bias, and to consider different perspectives and assumptions. By continuing multiple rounds of planning poker, the team can improve the accuracy and reliability of their estimates and plan their iterations more effectively. References: PMBOK Guide, 7th edition, page 309; Agile Estimation Techniques for the PMP Exam