input: DoubleClick for Publishers doesn't have master or companion ads. Instead, roadblocks are set up in a single ad/line item that contains all of the creatives for the roadblock. Roadblocks are set up in a line item's settings in the "Deliver creatives" drop-down list. (Learn how to roadblock creatives) [Term in DART for Publishers] 
output: Master ad The primary ad in a roadblock campaign. When a master ad serves as part of a roadblock, DART also serves a companion ad on the same web page. The master ad is always served first. Each master ad in your order can be associated with up to six companion ads, all of which inherit the master ad's targeting and delivery settings.