a. An alteration of the form of a word by the addition of an affix, as in English dogs from dog, or by changing the form of a base, as in English spoke from speak, that indicates grammatical features such as number, person, mood, or tense.

b. An affix indicating such a grammatical feature, as the -s in the English third person singular verb form speaks.

c. The paradigm of a word.

d. A pattern of forming paradigms, such as noun inflection or verb inflection.