Here are two links explaining the hand fasting ceremony. Son and future daughter-in-law are having a celebrant perform the ceremony and it will be a lasting one.
(cut and paste to view links)
There are two conflicting beliefs about the history of Handfasting:
"Handfasting" was the word used by the ancient Celts to describe their traditional trial-marriage ceremony, during which couples were literally bound together. The handfasting was a temporary agreement, that expired after a year and a day. However, it could be made permanent after at that time, if both spouses agreed.
"Handfasting" was the word used throughout the once-Celtic lands of Scotland and Northern England to refer to a commitment of betrothal or engagement. It was a ceremony in which the couple publicly declared their intention to marry one year and a day in the future. In 1820, Sir Walter Scott used the term to refer to a fictional sacred ritual that bound the couple in a form of temporary marriage for a year and a day. He wrote of it in his book "The Monastery:"
"When we are handfasted, as we term it, we are man and wife for a year and a day; that space gone by, each may choose another mate, or, at their pleasure, may call the priest to marry them for life; and this we call handfasting." 1,2