Co-ordinate, or double, articulation

In double articulation there are two simutaneous articulations of the same rank-that is to say, of the same degree of stircture, hence: stop+stop, fricative+fricative, or approximant+approximant.

We lable co-ordinate, or doulbe, articulations by means of either a plus sign or a hyphen: thus[ k͡p ]=bilabial+velar or bilabial-velar. Double articulated bilabial+velar sounds are sometimes referred to as 'labio-velar' or 'labiovelar'. This usage should be avoided, since the latinate prefixes labio-, apico- etc. refer strictly to lower articulators and should not be used to refer to the whole conjunct, lower+uper, articulation.

資料來源:
J.C.Catford, (2001), A Practical Introduction to Phonetics, Oxford University Press (P.100)