NUNC PRO TUNC is a Latin phrase meaning “now for then.” When it is included in an order of the Court it is essentially a means of making an act effective retroactively.
One common form the term crops up in is when an attorney asks for leave to file a document nunc pro tunc. This usually means that for a good reason or a bad reason, a filing deadline was missed. Under these circumstances the lawyer’s best hope is to argue that some extraordinary circumstance occurred that made timely filing impossible.
Other times the term is used more loosely to describe the timing when relief to a litigant should be effective. For example, if a special needs child is denied for a period certain relief he or she is otherwise entitled to, relief may be rewarded by the Court nunc pro tunc, meaning essentially that a back payment for arrearages is due to the child.
– BBC&B