Final answer:
Sexual activity outside marriage is called adultery when it involves married individuals, and infidelity when it includes those in committed relationships. Promiscuity refers to having multiple sexual partners, and polygamy refers to the practice of having multiple spouses.
Step-by-step explanation:
Sexual activity outside marriage is often referred to using different terms, depending on the context and behavior. Adultery usually refers to a married person having sexual relations with someone other than their spouse. Infidelity is a broader term that can also refer to engaging in sexual or romantic activities outside one's relationship, without the consent of their partner. Promiscuity is a term that can indicate having multiple sexual partners without necessarily having a committed relationship. Polygamy, however, refers to the practice of marrying more than one spouse and is a form of marriage rather than sexual activity outside of marriage.
Given the provided options, the terms closest to the definition of sexual activity outside of marriage are adultery and infidelity. However, 'adultery' is specific to married individuals, while 'infidelity' can apply to those in committed relationships, regardless of marital status. Promiscuity describes a pattern of behavior rather than a specific event or relationship status. Polygamy does not refer to sexual activity but rather to the sanctioned marital status with multiple partners.