What does a PushTopic define aside from the notification channel?

A PushTopic is a powerful feature in Salesforce that enables real-time updates to clients that are subscribed to it. The primary purpose of a PushTopic is to define a set of criteria to listen for changes in Salesforce data and generate notifications accordingly. This includes defining the specific events that will trigger a notification to subscribers.

By specifying what events will cause a notification, the PushTopic allows developers to control and filter the data that is pushed to subscribers. For instance, a PushTopic can be configured to notify clients only when certain records have been created, updated, or deleted based on specific conditions such as field changes or record types. This granularity ensures that clients receive only the relevant notifications they need based on the defined criteria, enhancing efficiency and relevance in data monitoring.

In contrast, the other choices focus on aspects that are not directly related to the core function of a PushTopic. The data format of notifications, the type of client that can subscribe, and user permissions are important aspects of the broader integration ecosystem, but they do not define what events trigger notifications. Instead, these are settings or configurations that may refresh the overall functionality and usability of the PushTopic but are not foundational to its primary purpose.