Closed-domain refers to a specific area or topic where a system, such as a chatbot or search engine, operates. In this context, the system is designed to provide accurate and relevant information within a limited scope, such as medical advice, customer support, or technical troubleshooting. This focus allows for more precise responses compared to open-domain systems, which handle a broader range of topics. In closed-domain applications, the data and knowledge are often curated and structured to ensure high-quality interactions. For example, a legal advice chatbot would be trained on legal terminology and case law, enabling it to assist users effectively within that particular field.