This book not only defines but also describes and discusses each of the concepts selected in relation to its theoretical, historical, and empirical background, with the aim of informing the reader about its place in the discipline, its origins, the purpose for which it was intended, and the extent to which it has been found useful. Arranged thematically in sections corresponding to chapter headings usually found in textbooks, this book could act as either a primary or secondary source for students wanting an accessible book to enrich their learning experience.