A "quack" refers to a person who pretends to have medical skills or knowledge but lacks proper qualifications. Often, quacks promote unproven treatments or remedies, which can be harmful to patients. They may operate in various fields, including alternative medicine, where they offer services that are not scientifically validated. The term can also describe someone who is deceitful or fraudulent in other professions. In the context of healthcare, quacks can undermine trust in legitimate practitioners and lead to serious health risks. It is important for individuals to verify credentials and seek advice from qualified professionals.