 Central concepts, you know, to understand any course, we need to know the language of that course. By language, I mean the central concepts that would occur and re-occur in that course, in discussion of that course. So, here our central concepts are defined, first of all, sex. So, in this course, whenever we will define sex, it will stand for our biology, our biological sex. We are born as male and female. We will also call it heterosexuality in this course. It is also called natural gender. Gender, this is the gender, natural gender that is usually used to organize society. Society is organized into males and females and after that roles and responsibilities are divided according to males and females. So, this is natural gender or that is sex. This classification that is based on our natural gender or sex, this is recognized all over the world. So, in most of the countries of the world, in most cultures of the world, this is the dominant concept of sex. Feminists support heterosexuality, the sexual relations between opposite sex between male and female, not between male and male or female and female. This is heterosexuality. Feminists, the political activists who favor justice and equality for women. They accept heterosexuality, but they are against the consequences, social consequences of heterosexuality. Because on the basis of sex, there are certain discriminations in society. So, another social group is transgender. Transgender activists, they do not recognize heterosexuality. They say that there are not only two gender categories. There can be different gender categories. Other categories are also possible. That is why we call them transgender, beyond gender, the recognized categories of gender. They are in favor of diversity in sexuality. Another term is grammatical gender. This is sex-based classification of nouns and pronouns. In English, you are familiar with that. Whenever we talk about pronouns, we say this is for feminine, this is for masculine, this is for neuter. Another concept is cultural gender. The cultural division of the society as men and women. It is according to the social norms, social division of work, social division of roles and responsibilities. That kind of gender is called cultural gender. Men and women as defined by culture. This is cultural gender. Then comes another term, sexuality. This is recent addition. Non-binary sex categories and ideology behind that non-binary concept of sex. So, these are basic, central concepts. We should be clear about definitions of these concepts. Because each of these concepts is related with different types of theory and ideology.