A "cold case" refers to a criminal investigation that has not been solved and is no longer actively pursued by law enforcement. These cases often involve serious crimes, such as homicides or missing persons, where leads have dried up, and no new evidence has emerged for an extended period. Cold cases can remain open for years, sometimes even decades, as new technology or information may eventually come to light. Advances in forensic science, such as DNA analysis, can help reopen these investigations, providing hope for families seeking closure and justice for their loved ones.