An example of a custom metric is?

A custom metric refers to a metric that is defined and used specifically for the unique needs or characteristics of a particular application or service. In the case of the provided example, "Users.posts.liked" is a custom metric that implies tracking a specific user interaction within the context of an application, likely a social media platform or similar service.

This metric is tailored to specific business logic and user behavior, emphasizing user engagement within the application. It reflects the application's unique data, which is critical for monitoring, analyzing user activity, and driving insights relevant to that particular application or service.

The other options represent system-level or infrastructure metrics typically provided by Datadog out-of-the-box. These metrics, such as memory usage or storage statistics, are useful for monitoring the overall health and performance of a system but do not represent custom measurements defined by the user for specific business needs. This distinction highlights the significance of "Users.posts.liked" as a tailored metric integral to understanding user engagement in a specific context.