Gender
More than any other term in the English language, the term "gender" is notoriously difficult to define.
Once upon a time, the term "gender" was a kind of generic term applied to the classification of male vs. female. In many languages, however, gender came to be applied to inanimate objects with no discernible connection with sexual function or orientation.
As if this were not confusing enough, a consensus built within polite society to agree to label a man "female," or a woman, "male," if a "sex-change" operation were performed on the genitals or other visible sexually-differentiated features of the person in question, perhaps in conjunction with establishing a regimen of hormone therapies, leaving all other distinguishing factors, such as chromosomal complement, cerebral characteristics or other factors unchanged (primarily because these differences remain outside of the competence of technology to alter).
Most recently, the terms "male," "female" and "other" have come to be assigned purely on the basis of how a given person would prefer to be regarded on any given day. Naturally this has led to some confusion in the use of public accommodations, particularly in large cities. Furthermore, traditional religions have tended to regard this post-modern cultural artifact as "the next ticking time-bomb," since so much of established religion, both in ritual and in creed, has been tied to the classical definition of these terms.
Indeed, historians of philosophy will recognize that this evolving state of affairs represents the ultimate triumph of the nominalist school over the realist school. Historians of ethics will recognize that it ensures the ultimate triumph of the doctrine of moral relativism and situational ethics. Religious historians will recognize in this the ultimate triumph of Gnosticism (and its cognates, including New Age). Finally, political historians will see in this the ultimate triumph of progressivism over conservatism.
As a result, it is no longer possible to discern the gender of a person with any guarantee of culturally-conditioned success. Furthermore, since the terms "male" and "female" no longer mean what they used to, and since "other" possible "genders" are regarded as possible and even culturally normative in some sense, it is no longer possible to give a succinct definition of the term "gender" to everyone's satisfaction.
As a result, we do not attempt to do so, here.