This document discusses morphology, which is the study of morphemes and how they combine to form words. It defines a morpheme as the smallest unit of meaning and outlines the criteria that morphemes must meet. The document explains that morphemes can be free or bound, and that bases and affixes are two types of morphemes. Specifically, it states that bases carry the principal meaning of a word and that prefixes, suffixes, and infixes are kinds of affixes that occur before, after, or within a base, respectively.