Grue

"Grue" is a term from philosophical discussions about how we categorize and predict objects based on observation. It describes a color that appears green before a certain time and, if an object has been observed up to that point, is expected to be green afterward—regardless of its actual color. The concept highlights the difficulty in defining properties like color when they depend on observation times and standards. Essentially, "grue" illustrates that some categories are based on specific conditions, which can complicate how we understand the nature of properties and the basis for scientific classification.