A milestone can be interpreted as:
- markers of reaching an identifiable stage in any task or the project
- Software release life cycle state
To identify milestones in Jira you can use the 'Label' type of field as #milestone.
Labels will be added or removed in the following scenarios:
- the task is changed into milestone -> label #milestone in Jira is added
- milestone into the regular task -> label #milestone in Jira is removed
- milestone into a parent -> label #milestone in Jira is removed
In order to generate labels when a milestone is created you need to configure the mapping in Global configuration - Task configuration.