In a blog post today, Twitter announced Tailored Audiences, a new way to define groups of existing and potential customers, and to connect them with relevant brand messaging. In principle, the service will target users on Twitter who have also visited a product or brand’s website, so as to provide a sense of relevancy to the ads being served. The goal is to find groups of existing target customers who have already expressed interest, and use Twitter to convert them into sales. Though it seems straight forward, Twitter wants to build the service out to include other forms of targeting in the future.