An Event Hubs namespace is a management container for event hubs (or topics, in Kafka parlance).
Namespace provides DNS Integrated Network Endpoint which refers to the way of securing with Event Hubs : Allow access from specific IP addresses, Allow access from specific virtual networks, Allow access via private endpoints.
Specific IP addresses : https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-ip-filtering
Specific Virtual Networks : https://docs.microsoft.com/en-us/azure/event-hubs/event-hubs-service-endpoints
Private Endpoints : https://docs.microsoft.com/en-us/azure/event-hubs/private-link-service