"Ventless" refers to appliances or systems that do not require external ventilation to operate. This means they can function without needing a chimney, ductwork, or other means to expel air outside. Common examples include ventless gas heaters and ventless dryers, which are designed to recycle air within a space. These systems are often used in areas where traditional venting is impractical, such as small apartments or homes without existing ductwork. While they can be convenient, it's important to ensure proper air quality and safety measures, as they may release moisture or gases into the indoor environment.