Player Pooling combines all of the players from specific age groups so that every player in the age group can identify as being part of an unified program rather than an individual team. Pool training/rostering allows the players to be challenged at their own individually developmentally appropriate levels.
What does that mean?
US Youth Soccer Director of Coach and Player Development Manual
What about teams?
Pooling is NOT a refusal to recognize the social benefit of team identity or team-building that can be a great child-hood experience.