Non-smoker is the everyday word for someone who does not smoke — it is the most common and neutral choice in conversation, signs, and workplace policies. Tobacco-free person is a broader and more formal term that also excludes smokeless tobacco, snus, and vaping, so it is common in health campaigns and official rules. Never-smoker is a narrower medical term used in research or by doctors to mean someone who has never smoked even one cigarette — it excludes former smokers, whom a non-smoker label might include. In everyday English, use non-smoker; in clinical writing, use never-smoker when precision about lifetime abstinence matters.
Non-smoker is formed by adding the prefix non- (from Latin non, meaning 'not') to the noun smoker. The word became common in the early 20th century, when public health campaigns and the rise of designated smoking areas created a need to distinguish people who do not smoke from those who do.