Sexologist John Money introduced the terminological distinction between biological sex and gender as a role in 1955. Before his work, it was uncommon to use the word gender to refer to anything but grammatical categories. However, Money's meaning of the word did not become widespread until the 1970s, when feminist theory embraced the concept of a distinction between biological sex and the social construct of gender. Today, the distinction is strictly followed in some contexts, especially the social sciences and documents written by the World Health Organization (WHO). However, in many other contexts, including some areas of social sciences, gender includes sex or replaces it. Although this change in the meaning of gender can be traced to the 1980s, a small acceleration of the process in the scientific literature was observed in 1993 when the USA's Food and Drug Administration (FDA) started to use gender instead of sex. In 2011, the FDA reversed its position and began using sex as the biological classification and gender as "a person's self representation as male or female, or how that person is responded to by social institutions based on the individual's gender presentation." In non-human animal research, gender is also commonly used to refer to the physiology of the animals.
In linguistics, grammatical gender is a specific form of noun-class system in which the division of noun classes forms an agreement system with another aspect of the language, such as adjectives, articles, pronouns, or verbs. This system is used in approximately one quarter of the world's languages. In these languages, most or all nouns inherently carry one value of the grammatical category called gender; the values present in a given language (of which there are usually two or three) are called the genders of that language. According to one definition: "Genders are classes of nouns reflected in the behaviour of associated words."
Common gender divisions include masculine and feminine; masculine, feminine and neuter; or animate and inanimate. In a few languages, the gender assignment of nouns is solely determined by their meaning or attributes, like biological sex, humanness, animacy. However, in most languages, this semantic division is only partially valid, and many nouns may belong to a gender category that contrasts with their meaning (e.g. the word for "manliness" could be of feminine gender). In this case, the gender assignment can also be influenced by the morphology or phonology of the noun, or in some cases can be apparently arbitrary.