Save The Date
A save the date is similar to an invitation, except it is sent well in advance of the formal invitation.
Its purpose is to give your guests an opportunity to learn the date of your wedding, arrange for time off work if needed, organize childcare and to make travel arrangements.
Unlike an invitation, it does not contain the precise location, exact time of the ceremony, or any other wedding information and it is sent out digitally.
Essentially, it is a way of keeping the guests in-the-know about when and where your wedding is, while you work out the finer details.