What is planning poker?
Planning poker (also called scrum poker) is an agile estimation technique where each person on the team secretly picks a card with the effort they expect for a story. Cards are revealed at the same time, so the first opinion does not anchor everyone else.
When estimates differ, the highest and lowest voters explain their reasoning. That conversation usually uncovers risks and different readings of the work, which is where most of the value lies. Then the team votes again until it converges.