An affix is a morpheme that's attached to a stem to form a word. Affixes may be derivational, like English -ness and pre-, or inflectional, like English plural -s and past tense -ed. They are bound morphemes by definition; prefixes and suffixes may be separable affixes. Positional categories of affixes Affixes are divided into several categories, depending on their position with reference to the stem. Prefix and suffix are extremely common terms. Infix and circumfix are less so, as they're not… (More on Affixation)