Science communication is a growing area of practice and research. During the past two decades, the number of activities, courses, and practitioners has steadily increased. But what actually is science communication? In what ways is it different to public awareness of science, public understanding of science, scientific culture, and scientific literacy? The authors review the literature to draw together a comprehensive set of definitions for these related terms. A unifying structure is presented and a contemporary definition of science communication positioned within this framework. Science communication (SciCom) is defined as the use of appropriate skills, media, activities, and dialogue to produce one or more of the following personal responses to science (the AEIOU vowel analogy): Awareness, Enjoyment, Interest, Opinion-forming, and Understanding. The definition provides an outcomes-type view of science communication, and provides the foundations for further research and evaluation.