The ROS Parameter Server is a central repository for storing, retrieving, and setting parameters at runtime. It is used to store various data such as configuration values, calibration values, and other data that can be accessed by multiple nodes.
For example, a robot may have several sensors that need to be calibrated at startup. Instead of having each node query the calibration values from a file, the values can be stored in the Parameter Server and accessed by the nodes. This allows for a single source of truth for the calibration values and makes it easier to update them.