You use business day labels in the closing activity for a calendar day. Labels can mark a milestone day or specify the purpose of the day.
When you add Day Labels to a template, they are copied to schedules created from the template.
When schedules are opened, you see day labels in:
Calender views against the day they are marked
Task List views and Gantt views in the start or end date of tasks
BI dashboard, My Worklist, and schedule task, in start date and end date columns
Status overview, when focused on date, its information is displayed along with day label.