We need to clarify the difference between terms that are used in various parts of the professions that deal with voice.
These are my “takes” on things. Check into these and draw your own conclusions.
Vocal folds are the medical name of the ligaments that vibrate in the larynx to make sound. Vocal cords is the term still used (but fading) in the teaching (pedagogic) community.
The larynx is a cartilage and a joint. This is a medical term used in the other professions. In lay terms the larynx is sometimes called the “voice box”.
The term “falsetto” is a pedagogic term to describe a particular kind of sound. The behavior of the vocal folds in this sound is generally referred to as “loft” in voice science and is caused by the vocal folds touching loosely. If you define falsetto as a production that has little vocal fold contact at the bottom of the folds and acoustically has most of its energy in the fundamental (Fo), then everybody can produce it.
The term head register, as well as the terms head resonance, head tone, head mechanism, light mechanism and upper register are all pedagogic terms. They refer to a sound produced by the Crico Thryoid action upon the vocal folds that stretches and thins them to raise pitch by increasing length and tension, thereby causing only the upper edges of the folds to meet. This could be called CT behavior.
The term chest register, as well as the terms chest resonance, chest tone, chest mechanism, heavy mechanism, and lower register, are all pedagogic terms. They refer to the sound produced by the main body of the vocal fold (the vocalis) that brings the full depth of the fold into closure for vibration. This could be called TA behavior.
The terms breath support and breath management are pedagogic terms. The voice science term is sub-glottic pressure but also references trans-glottal airflow. Medicine uses both.
The term for changes in volume in music is dynamics, in pedagogy is intensity and in science is decibel level or sound pressure level.
In physics, resonance is the tendency of a system (usually a linear system) to oscillate with larger amplitude at some frequencies than at others. In pedagogy, it means different things to different people.
People “discover” things as they sing. They teach what they “discover” to others who are supposed to “understand” what the teacher means. If the teacher has not run these discoveries by any scientist or doctor, the teacher doesn’t really know if his or her conclusions are meaningful or valid. That does not, however, stop most of them from dealing with the information as they understand it as if it were “true”.
Singing teachers like to make up terms (truthfully, everyone does it, in all the professions). This is not helpful to anyone. If everyone would make an attempt to stick to the terms that are already out there (by first finding out what they are), and trying to use them or comment upon why the usage should change, instead of coming up with a new word for “wheel”, everyone would benefit.
If you are teaching and you make up something and then give what you have made up names or create a term for it, PLEASE STOP!!!!!!! Find out what the words are that already exist, and why they exist, that are standard lexicon in whatever profession you are in and/or the other related professions and use those words.