How do you identify a definition as being "actual"? Why are the Myers-briggs authors the authority on introversion? Many people consider the MBTI to be bunk sci

How do you identify a definition as being "actual"? Why are the Myers-briggs authors the authority on introversion? Many people consider the MBTI to be bunk science, and the term "introvert" has been around for much longer than the MBTI. EDIT: Also, why does there have to be just one definition anyway?