Classify the Following Definition According to Its Use: to Reduce

Short Answer

Classify the following definition according to its use: to reduce vagueness, to introduce or explain a new or unusual word, to evoke an attitude about something, or to accomplish some other purpose.
"Subduction zone: In interpretations of plate tectonic theory, a belt along the under-margin of a continental plate, where the colliding oceanic plate descends toward or into the mantle."-Robert M. Norris and Robert W. Webb, Geology of California