A more thorough explanation:

A bill of mortality is a historical record that documents the number of deaths that occurred in a specific area or district. These bills were created in England from the late 16th century to the 19th century as a way to keep track of highly contagious diseases, such as the plague.

For example, a bill of mortality might list the number of deaths in a particular parish or town during a specific week. This information was used to monitor the spread of diseases and to help authorities take appropriate measures to prevent further outbreaks.

Overall, bills of mortality were an important tool for public health officials in the past, and they provide valuable insights into the history of disease and mortality rates in different regions.