Planning Poker is a technique used to estimate effort for tasks in Agile software development. It involves each team member privately selecting a planning poker card representing their estimate for a task. The cards have Fibonacci numbers written on them. The cards are then revealed and discussed if estimates differ, until consensus is reached. Once estimates are established, the team's velocity (amount of work completed per sprint) can be used to predict future release dates. Planning Poker works well because it leverages the wisdom of crowds and averages individual estimates for more accurate results.