Mobility domains and mobility groups are concepts used in wireless networking to manage client roaming and security contexts. When Wireless LAN Controllers (WLCs) are in the same mobility domain, they can communicate with each other, allowing clients to roam seamlessly between APs managed by different controllers. Mobility groups further refine this by constraining the distribution of a client's security context, which includes authentication and encryption keys, and by managing AP failover between controllers. This ensures that a client can maintain a secure and stable connection as they move throughout the network.