calendar

A definition of working time and non working time (in shift patterns) that can be applied to individual resources working on the project, or to the project and the tasks within it.

The default calendar is called a base calendar.

Calendars are edited or created within the Change Working Time dialog box (Tools..Change Working Time). The Organizer allows this component to be shared between projects.

SOURCE; projectlearning.net

The calendar used in developing a project schedule. This calendar identifies project work days, and can be altered so weekends, holidays, weather days, etc., are not included.

SOURCE: apm.com