The prefix "re-" in the word "reunion" comes from Latin, where it means "again" or "back." In this context, "union" refers to a joining or coming together of people or things. Therefore, "reunion" essentially means "coming together again."
People use the term "reunion" to describe events where individuals who have been separated—whether for a long time or just temporarily—come together again. This could refer to family reunions, school reunions, or any gathering of people who were once part of a group but have since gone their separate ways. The "re-" emphasizes the idea of re-establishing connections and relationships that may have been lost or altered over time.