Background "Tobacco-free" nicotine (TFN) e-cigarettes and nicotine pouches containing synthetic nicotine are increasingly available. The term TFN may lead to reduced risk perceptions and increased use intentions relative to tobacco-derived nicotine products. Effectively communicating messages about TFN may depend on the public's ability to differentiate TFN from tobacco-derived nicotine. Our goals were to examine knowledge about the source(s) of nicotine in commonly used products and beliefs about what TFN means. Methods In 2021 we surveyed 2464 young adults (18-25 years) online. Participants reported whether cigarettes, smokeless tobacco, e-cigarettes, and nicotine pouches contain nicotine that comes from tobacco (always, sometimes, never). Correct responses were "always" for cigarettes/smokeless and "sometimes" for e-cigarettes/pouches. Participants also reported "what [they] think TFN e-cigarettes/vapes contain" (nicotine only; tobacco only; both nicotine and tobacco; neither nicotine nor tobacco). We ran unadjusted and adjusted models examining correct responses for nicotine source and TFN contents by past-month product use status (cigarettes, smokeless, e-cigarettes, pouches). Results Rates of correctly identifying nicotine source were modest (23.6% pouches-61.9% cigarettes). Except smokeless tobacco, using a given product was associated with identifying its nicotine source correctly in unadjusted models. Participants reported "TFN" means a product contains nicotine only (57.8%), tobacco only (10.8%), both (14.1%), or neither (17.1%). Conclusions There is confusion about the source of nicotine in products, and many young adults incorrectly interpreted TFN to mean something other than containing nicotine but no tobacco. Regulatory efforts may be needed to restrict using the term "tobacco-free nicotine" on product labeling and advertising.