A more thorough explanation:

The public-interest exception is a principle that allows an appellate court to consider and decide a moot case, even though such decisions are generally prohibited. This exception applies if the case involves a question of considerable public importance, the question is likely to arise in the future, and the question has evaded appellate review.

For example, if a court case involving a controversial law is dismissed because the law has been repealed, the public-interest exception may still apply if the law is likely to be reintroduced in the future. The court may decide to hear the case and issue a ruling on the constitutionality of the law to provide guidance for future cases.

Another example is a case involving a public health crisis, such as a pandemic. Even if the immediate crisis has passed, the court may still hear the case to provide guidance on how to handle similar situations in the future.