Some of the terminology out there to describe vocal registers can be very confusing because the terms “chest voice” and “head voice” can mean different things to different people - both male and female. There is a certain convenience in using these terms, especially when my students understand these terms in regards to whatever they are working on, but if I have a preference, I like the Thurman and Welsh model from their 5 volume set of books called Bodymind and Voice: Foundations of Voice Education which describes the structure of every voice as follows:
What the chart shows is 5 distinct vocal registers which are common to both men and women, ranked in terms of their pitch. These registers overlap to a certain degree and that when you enter the orange and red zones of a register, an accomplished singer would want to transfer up to the next register and avoid unnecessary strain. Straining or pushing at the top end of a register is otherwise known as “belting”.
The tonal quality of each register can be quite different, particularly between the natural and false vocal registers. A professional singer would optimally want to move into the next register by mixing or gradually blending the adjacent vocal registers together so that there is no abrupt change. The muscle control for this requires practice with exercises that bridge the two vocal registers. Generally for both men and women, the most difficult register change to negotiate is the one between the upper and falsetto (men) or flute (women) registers.
In the convenient terms of head and chest voice, the natural voice registers are generally considered to be chest voice and the false voice registers are called the head voice, Where the confusion can occur is when singers mistaken their lower register for their chest voice and upper register as their head voice, particularly beginners who have trouble going between these two registers when they start out.
There can also be confusion about defining head voice and differentiating it from a common misunderstanding of falsetto voice. It is possible to produce sound in the falsetto/flute range in two different ways; with connected vocal chords and unconnected vocal chords. With connected falsetto the vocal chords approximate together and engage fully to create sound allowing greater resonance and volume control. In the case of unconnected falsetto, the vocal chords remain apart with only the fringe areas of the chords vibrating to make sound. When additional airflow is introduced to try increase the volume of this voice, the vocal fringes blow apart, creating a more breathy airy sound, hence the term unconnected. This has been demonstrated with microcameras inside singers’ mouths and you can find various videos on youtube showing the difference in action. Nonetheless there is a convention which says that connected falsetto is “head voice”, whereas unconnected falsetto, the weaker and airier of the two is “falsetto voice”, despite the pitch range being the same. It should be noted that while there is a physical difference between the production of these two sounds, Thurman and Welsh still classify them both as being part of the falsetto register.
There is a fantastic video by Brisbane contemporary singing teacher Dr. Daniel Kay that explains the vocal registers very clearly, using the Thurman and Welsh model which is definitely worth watching. Find it here: https://www.youtube.com/watch?v=CAGR81QFIj0
Hope that this helps you navigate through your own vocal registers.