Heterosexuality
Romeo and Juliet, a classic example of a heterosexual couple.
Heterosexual people love people of the opposite gender. A heterosexual man loves women. A heterosexual woman loves men. Another less formal word for heterosexual is straight.
People who are not heterosexual may be homosexual, bisexual or asexual. Many people in Western society are heteronormative, which means that they believe that heterosexuality is better than other forms of sexuality. This often leads to discrimination.
In the Catholic Church and many Christian churches as well as in Islam and Judaism, a marriage can only be made in a heterosexual pair - man and woman. Marriage that is done in homosexual pair is often seen as a serious sin by those religions.