ZHR, or Zenith Hourly Rate, is a measure used in astronomy to indicate the number of meteors that can be expected to be seen per hour when observing at the peak of a meteor shower. This rate helps astronomers and enthusiasts gauge the intensity of a meteor shower, allowing for better planning of observation times. The ZHR is calculated under ideal conditions, meaning a clear sky and no light pollution. It serves as a standard reference for comparing different meteor showers, such as the Perseid or Geminid showers, which are known for their high ZHR values during their peak activity.