What is the meaning of the terms sustainable development and sustainability? The relevant discourse usually refers to the denotation of sustainable development. However, what about the many people not familiar with the concept as presented in Agenda 21? In contrast to denotation, most people have a connotation of sustainable development, even when they don’t know much about it. Amongst the general importance for communicating the concept, it is especially relevant for the UN-decade for education for sustainable development. This is because most people that begin to learn about the concept have a much clearer connotation of sustainable development. This article identifies the connotation of the two terms in Germany (nachhaltige Entwicklung and Nachhaltigkeit). It was found that the connotation of the two terms is positive in general. As expected, it is more positive for people that usually support the concept, such as environmentalists. There is a difference between the connotation of sustainable development and sustainability, but only for people that do not know the terms. This difference decreases significantly for people that know more about it, which indicates a synonymous use of the two terms in Germany.