A more thorough explanation:

An alderman is a member of a city council or other local governing body. They are also sometimes called alderpersons.

For example, in a city council, there may be several aldermen who are responsible for making decisions about local laws and policies.

Historically, there were different types of aldermen with specific roles. For instance, an aldermannus civitatis vel burgi was an alderman of a city or borough, while an aldermannus hundredi seu wapentachii was an alderman of a hundred or wapentake.

The term "alderman" is still used today in many cities and towns around the world, including in the United States, Canada, and the United Kingdom.