Prometheus is an open-source monitoring and alerting platform that collects and stores metrics as time-series data. It is also considered an open-source systems monitoring and alerting toolkit. Prometheus is used to collect and store metric data from client applications, and this data is then available to be analyzed and visualized using Grafana.

Grafana, on the other hand, is an open-source data visualization and monitoring platform that allows users to create, explore, and share dashboards and data with teams. It provides out-of-the-box support for Prometheus, and the combination of Prometheus and Grafana Agent gives users control over the metrics they want to report, where they come from, and where they’re going. Grafana dashboards consist of visualizations populated by data queried from the Prometheus data source. The PromQL query filters and aggregates the data to provide users with the insight they need.

In summary, Prometheus is a core technology for monitoring and observability of systems, while Grafana is a data visualization and monitoring platform that allows users to create, explore, and share dashboards and data with teams. Prometheus collects and stores metrics as time-series data, while Grafana allows users to visualize the data stored in Prometheus and other sources.