Line item An advertiser's commitment to purchase a specific number of ad impressions (CPM), user clicks (CPC), or time (CPD), on certain dates at a specified price. A line item: Specifies where an advertiser's ads will appear. May specify an ad's target audience. May specify when an ad may be shown. Is associated with one or more ad creatives. May be able to display creatives of multiple sizes. (Learn how to create a line item) [Term in DART for Publishers] 
Ad Any content in a website that acts as a commercial device to carry a message or attract a user. This content typically takes the form of an image or text, but can also use multimedia effects.