From the very excellent book, A Spectrum of Voices:
“In my opinion, posture is a word that can be limiting because it can infer stillness and a single correct position. I find the term body-use—which originated with the Alexander Technique–more useful. This terms enlarges the student’s concepts to include the whole body and it emphasizes ease, freedom, and flexibility of movement. I think singers should realize that they never really stand still–their body is continually moving whether the movement is small or large. Even breathing is movement!”
I find this last point particularly salient–we would demand a refund if a violinist playing a concerto stood still and sawed away without any expressive movement. A singer’s body must be free to respond to the music, without trending too far in the opposite direction of mannered or phony movement. Wall’s assertion that the term “posture” infers stillness is also wise–and too often we see singers who yearn to find the right posture and “hold” it. Words have power, as do their connotations.