Explanation: Box 1: custom topic "Topics. The event grid topic provides an endpoint where the source sends events(...)Custom topics are application and third-party topics" Box 2: event subscription Event subscriptions. A subscription tells Event Grid which events on a topic you're interested in receiving. When creating the subscription, you provide an endpoint for handling the event. https://learn.microsoft.com/en-us/training/modules/azure-event-grid/2-event-grid-overview