The articulatory process whereby the pronunciation of a word or morpheme changes when it is followed immediately by another (especially in fluent speech) WordNet 3.0 & Open English WordNet

Sandhi is a cover term for a wide variety of sound changes that occur at morpheme or word boundaries. Wikipedia

Any of a wide variety of phonological processes that occur at morpheme or word boundaries, such as the fusion of sounds across word boundaries and the alteration of sounds due to neighboring sounds or due to the grammatical function of adjacent words. Wiktionary

Phonological process. Wiktionary (translation)