KoenigLookup is a commonly used name for ArgumentDependentNameLookup, also known as Argument Dependent Lookup (ADL). It is a feature of CeePlusPlus. One of the CeePlusPlusIdioms.
See ArgumentDependentNameLookup. This page is here for those who find the name KoenigLookup first.
CategoryLanguageFeature CategoryCpp CategoryIdiom