Open play is drop-in pickleball. No fixed roster, no entry fee beyond court time, no bracket. You arrive during a posted window, put your paddle in the queue, and play with whoever is next.
Most clubs and parks run it on a schedule, sometimes split by skill level. The appeal is that it costs you nothing to commit to: you can show up late, leave early, and still get games.
The tradeoff is that open play runs on whatever system the group has agreed on, and those systems break down as the group grows. Twelve people on two courts is easy. Twenty-four is a queue.