Singing in falsetto or head voice? Singing with falsetto voice and the head voice is not the same thing. It is a very common misconception amongst singers who think that a falsetto voice and a head voice are the same.
Falsetto is the lightest vocal production made by the human voice. It is limited in tonal variation, strength and vocal tonal dynamics. There is usually a "jump", "disconnect" or even a break between your chest (speaking) voice and your falsetto note.
A much distinguished vocal coach and voice trainer, Randy Buescher of Chicago once defines falsetto as, "a co-ordination where the outer layer of the vocal cord (mucosa, i.e. internal skin or muscular covering) is vibrating, creating sounds, but without engaging the actual musculature of the cord.
Also, there exists no medial compression. That means that during the vibratory cycle, the cords never fully approximate during singing a falsetto note.
However, the cords do approximate in a head voice, but the vibration of the cord moves away from the full depth of the vocal cord (chest voice) to a pattern that involve less and less depth of vocal cord as you ascend towards the upper end of your voice range. The highest and top most notes of your range involve only the vocal ligament.