What does mother has precedence?

To avoid the problem of both parents selecting the same week for vacation with the children, parents often say who has precedence when choosing a vacation.  Since your schedule says that Mother has precedence in odd years and Father in even years, if you both selected the same week, Mother would be able to take vacation when she wants to this year and Father would have to select a different vacation period.  Next year, Father would get first choice in the event that you both selected the same time period.