**Core Concept**
Adultery is a form of extramarital sex that involves a married person engaging in sexual activities with someone other than their spouse, with or without the spouse's consent. This concept is relevant in the context of forensic medicine and medical ethics, particularly in cases of sexual assault or infidelity.

**Why the Correct Answer is Right**
In the context of the question, adultery refers to sexual intercourse between a married person and someone other than their spouse. The key aspect here is the involvement of a married person, and the fact that the intercourse occurs with or without the consent of the spouse. This definition is crucial in distinguishing adultery from other forms of extramarital sex.

**Why Each Wrong Option is Incorrect**
**Option A:** There is no widely accepted definition of "extramarital sex with consent" as a separate legal or medical term.
**Option B:** "Infidelity" is a broader term that encompasses any form of sexual unfaithfulness, not limited to adultery.
**Option C:** "Bigamy" refers to the act of marrying someone while still being married to another person, which is not relevant to the scenario described.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, distinguishing between different forms of extramarital sex can be crucial in establishing the facts of a case, particularly in cases of sexual assault or infidelity. Adultery is often considered a form of marital misconduct, and its definition can vary depending on the jurisdiction or cultural context.

**Correct Answer: D. Adultery**