A more thorough explanation:

The single-source requirement is a legal term used in the common-law tort of false advertising. It refers to the necessity of proving that the plaintiff is the only supplier of the genuine goods in question and that buyers would have purchased the plaintiff's goods if they had known the true nature of the defendant's goods.

For example, let's say that Company A sells organic apples, and Company B sells conventional apples. If Company B falsely advertises their apples as organic, Company A would need to prove that they are the only supplier of organic apples and that customers would have bought their organic apples instead of Company B's conventional apples if they had known the truth.

The single-source requirement is a narrow exception to the common-law rule that the tort of false advertising only applies in cases of passing off, trade defamation, and trade disparagement. It is designed to protect businesses that have invested time and resources into creating a unique product or brand from unfair competition.