Ceilometer is a component of the OpenStack cloud platform that collects and stores data about the usage of resources within an OpenStack deployment. It is a metering and monitoring service that provides information on the utilization of compute, storage, and networking resources, as well as the consumption of OpenStack services like Nova, Cinder, and Neutron.

Ceilometer collects data through various sources, such as the OpenStack APIs, notification messages, and polling mechanisms. It stores the collected data in a database, which can be queried and analyzed to gain insights into resource usage, performance monitoring, and capacity planning.

With Ceilometer, users can track resource usage, monitor performance, and generate reports on resource utilization. It provides a rich set of meters, which are predefined measurements of resource usage, such as CPU utilization, memory usage, network traffic, and storage usage.

Ceilometer also supports alarms and notifications, allowing users to set thresholds and receive alerts when certain conditions are met. This helps to proactively monitor and manage resource usage within an OpenStack environment.

Overall, Ceilometer is an important component of OpenStack for metering and monitoring resource usage, enabling users to optimize their infrastructure, improve performance, and ensure efficient utilization of resources.