The present studies of coronoid systems is a natural continua- tion of the corresponding studies of benzenoid systems. Both topics are rooted in organic chemistry through certain polycyclic conjugated hydrocarbons, which are the chemical counterparts of the systems in question. HO'v'Tever, the scope of the present work and corresponding works on benzenoids goes far beyond a chemical motivation. These works are classified under mathematical chemistry, a relatively new designa- tion. The book is supposed to have an interest for organic chemists within certain specialities, but still more for theoretical and mathe- matical chemists. The last category has been characterized as enfants terribles in the foreword of the first issue of the Journal of Mathe- matical Chemistry (1987). Finally, this book may have a considerable interest for mathematicians within combinatorics and gra~h theory. It is supposed that the book will be most useful for researchers, including graduate students, in the pertinent fields. The text contains no advanced mathematics whatsoever and should as such not represent any barrier even for undergraduate students. Here we wish to make some comments on the terminology, which is not standardized and is partly controversial in this field of topolo- gical studies of polyhex (benzenoid and coronoid) systems.