Required Boolean. If TRUE, the field must have value assigned to it before an item that is created using this content type ...

Required Boolean. If TRUE, the field must have value assigned to it before an item that is created using this content type can be saved. If an empty field value is given in a form post, either the standard required-field text or an explicitly specified message (that is, via  tags) is displayed in the error form. This validation is handled by the client only (the database always allows NULL for all user-defined fields).