Planning Poker is a team activity for sizing User Stories.
Planning Poker is played any time the team would like to size a User Story. Events it is commonly played at include backlog refinement meetings and during Sprint Planning.
To play Planning Poker you'll need a pack of Planning Poker cards; these can either be ones that you've made yourself or purchased. You'll need enough cards for one set per team member.
The following set uses T-shirt sizes:
Another approach uses a modified Fibonacci sequence:
The Fibonacci sequence ...