Reduplication in linguistics is a morphological process in which the root or stem of a word (or part of it) or even the whole word is repeated exactly or with a slight change.
Reduplication is used in inflections to convey a grammatical function, such as plurality, intensification, etc., and in lexical In linguistics, an alternation is the phenomenon of a phoneme or morpheme exhibiting variation in its phonological realization. Each of the various realizations is called an alternant. The variation may be conditioned by the phonological, morphological, and/or syntactic environment in which the morpheme finds itself.
Alternations provide linguists with data that allow them to determine the allophones and allomorphs of a language's phonemes and morphemes and to develop analyses determining the distribution of those allophones and allomorphs.