Here's a breakdown:

* Temperature: Measured in Kelvin (K), it represents the star's surface temperature. Hotter stars are located on the left side of the diagram, while cooler stars are on the right.

* Luminosity: This refers to the total amount of light a star emits. Brighter stars are located at the top of the diagram, while dimmer stars are at the bottom.

The H-R diagram is a powerful tool for astronomers because it reveals important relationships between a star's physical properties and its evolutionary stage.