The Latin phrase in re is used in legal cases to denote a case when there is no opposing party, as may happen in a situation like a change of name, where a person files paperwork to have a court order issued for a name change and no one opposes. The Latin translates as “in the matter of” or “in regards to” and people sometimes use this phrase outside of legal settings when they want to refer to a matter. In legal systems where the use of Latin is frowned upon in favor of plain language, people may simply say “in the matter of.”
There are a number of reasons why a case can come to court without an adverse party. Some cases involve situations where a court order is needed, but there's no particular reason to oppose it, like requests for guardianships. Sometimes, people go to court to ask for clarification on a legal matter, like requesting that a judge clarify the standard of proof for a given case, and the government declines to contest in court, turning the matter into an in re case.
Cases will be listed on the docket as in re and may be open to the public unless there is a compelling reason to close the court. People can attend these cases, listen to arguments, and read the opinion of the judge at the close of the case. The case is also filed in the proceedings of the court and may be referenced in the future, an especially common situation when people go to court because they want guidance on a legal issue.
While people often think of the court system as adversarial, in part because many legal systems are set up this way, court cases do not necessarily have to be adversarial in nature. Even when multiple parties are involved, they may be working towards the same resolution or end goal. Parents who work out a custody agreement and take it to court to get a court order, for example, would file in re, reflecting the fact that no one opposes the case.
The use of legal Latin like in re is on the decline in many regions of the world. While the legal profession has traditionally applied Latin for many formal terms, some people feel it creates jargon that makes it needlessly difficult to understand legal issues. A push towards plain language in some regions of the world has led to an increasing decision to use English or other common languages in the court system.