The crossword solution for the term 'Requirement of Custom or Etiquette' is 'Formalities'. Formalities are a set of rules and conventions that dictate how people should behave in certain situations. They are often based on social customs, cultural norms, and etiquette. Formalities can range from simple courtesies such as saying 'PLEASE' and 'thank you' to more complex protocols such as bowing and addressing someone with a title. Formalities are important in many contexts, including business, politics, and religion.