A more thorough explanation:

A nuncio is a representative of the Vatican in a country that has diplomatic relations with it. They are like ambassadors, but specifically for the Pope. The word comes from the Italian word "nunciare," which means "to announce."

In the past, the word "nuncio" was also used to refer to a messenger.

Example 1: The Pope sent a nuncio to meet with the President of the United States to discuss important matters between the two countries.

Example 2: In the 16th century, a nuncio was sent to England to try to convince Queen Elizabeth I to return to the Catholic Church.

These examples illustrate how a nuncio is a representative of the Vatican who is sent to other countries to represent the Pope and the Catholic Church. They are like ambassadors, but specifically for the Vatican.

The term "nunc pro tunc" is also related to the word "nuncio." It is a Latin phrase that means "now for then." In legal terms, it refers to something that has retroactive legal effect. For example, a court might enter a nunc pro tunc order to correct a clerical error in a record. This means that the correction is made as if it had been done on the original date, even though it is being done later.