First-party data is information collected directly and stored by website publishers, retailers and other types of companies about their site visitors or customers. Because companies with this information have a prior relationship with their customers, they are able to use this first-party data -- which may include names, addresses, phone numbers, site-interaction data and information about products purchased -- to communicate directly with them. First-party data is what is stored in customer-relationship-management and loyalty-program databases.

Brian Krick, head of search and biddable at Essence, a digital ad agency

"First-party data is information that you own about your customers. This information is created on systems that you own or lease, with the understanding that you the advertiser, and not the provider of the software or any other third party, have exclusive rights to that data. However, first-party data isn't as 'free' as people often claim. There are costs associated with creating, maintaining, and utilizing it -- costs in ad servers, CRM and web-analytics systems. It's really about maximizing the return from that investment."