In trademark law, a source is the unique manufacturer or service provider from whom a trademark originates. When a consumer sees a trademark, he/she knows the product bearing that trademark is from the same source as all other products bearing the same mark.
It is not necessary that the hypothetical consumer knows the actual name of the manufacturer or service provider. All that is necessary is that the consumer knows the products bearing one mark are from one source, while the products bearing another mark are from a different source. For example, BETTY CROCKER receives trademark protection, even if nobody knew that the source of Betty Crocker products was actually General Mills, Inc., the company that owns the BETTY CROCKER trademark.
The entire purpose of trademark law hinges on the ability of a trademark to identify a unique source. If one mark is related enough to another mark, in terms of look, sound, meaning, and use, then they no longer function to identify a single source, and thus cease to function as a trademark For this reason, a trademark is also referred to as a source discriminator, since it serves to help consumers discriminate between brands when making purchasing decisions.