Cuddon, J.A. A dict. of literary terms and literary theory, 1998 (didactic. Any work of literature which sets out to instruct may be called didactic. The Middle Ages produced the bulk of didactic literature in Europe and most of it was in verse.)
Baldick, C. The Oxford dict. of literary terms, 2008 (didactic. Instructive; designed to impart information, advice, or some doctrine of morality or philosophy. Much of the most ancient surviving literature is didactic, containing genealogies, proverbial wisdom, and religious instruction. Since the ascendancy of romanticism and aestheticism in the 19th century, didactic writing has been viewed unfavourably as foreign to true art.)
LCSH, Oct. 21, 2014 (Didactic drama)

Plays that are intended to be instructional.