In chapter 5, we had a look at observability backends. Essentially, these are specialized time series databases (TSDBs), general-purpose relational databases with a TSDB extension, or columnar data stores that are able to store logs, metrics, and traces. Once you have ingested the signals in a backend, you can use the backend to answer observability questions, usually referred to as querying. This process might be a declarative one, such as is the case with SQL or PromQL, or an imperative one, where you, for instance, tell a traces backend to look up a span by root span ID.
But the storage of signals and being able to query them are only means to an end. Observability is about understanding the system and getting actionable insights from the telemetry signals collected and ingested. So what you really want as a user of an observability solution is to ask ad hoc questions and get (timely) answers.