Coarticulation in phonetics refers to two different phenomena:

• the assimilation of the place of articulation of one speech sound to that of an adjacent speech sound. For example, while the sound of English normally has an alveolar place of articulation, in the word tenth it is pronounced with a dental place of articulation because the following sound, , is dental.
• the production of a coarticulated consonant, that is, a consonant with two simultaneous places of articulation. An example of such a sound is the voiceless labial-velar plosive found in many West African languages.

Phonetics | Assimilation