Questions: An event that is perceived as threatening or challenging is known as a stressor.

The answer is the first one: stressor.

Explanation for each option:

• Stressor: This is the correct answer. A stressor is any event or situation that is perceived as threatening or challenging, which can trigger a stress response.
• Distress: This refers to negative stress, which can be harmful and lead to anxiety or other negative outcomes. It is not the term used to describe the event itself.
• Eustress: This is positive stress, which can be motivating and beneficial. Like distress, it describes the type of stress rather than the event.
• Stress: This is the body's response to a stressor, not the event itself.

Summary: The term used to describe an event that is perceived as threatening or challenging is "stressor."