Open-domain refers to a type of system or application that can handle a wide range of topics and questions without being limited to a specific area. This means that users can ask about anything, from science to history to pop culture, and the system is designed to provide relevant information or responses. In the context of artificial intelligence, open-domain systems often utilize natural language processing to understand and generate human-like responses. Examples include chatbots and virtual assistants that can engage in conversations on various subjects, making them versatile tools for information retrieval and user interaction.