Which word describes the act of indulgence in sexual activity?

The term that best describes the act of indulgence in sexual activity is "lechery." It refers to excessive or inappropriate sexual desire or behavior, often characterized by a lack of restraint or morality. In various contexts, lechery can connote lustfulness and a preoccupation with sexual pleasures, suggesting a strong focus on indulgence in sexual activity.

In contrast, the other words do not relate to sexual indulgence. "Lithe" refers to someone who is flexible or graceful, often in physical movement. "Libel" pertains to a false and malicious statement that damages a person's reputation, typically in written form. "Languid" describes a state of weakness or fatigue, often marked by a lack of energy or vitality, rather than any association with sexual activity. Therefore, lechery stands out as the appropriate choice, specifically relating to the indulgent attitude towards sexual desires.