Definition
Run of site (ROS) is a phrase used to define inventory (page loads) that publishers are unable to forecast ahead of time. As a result of this they don’t have advertiser spending lined up. This causes them to dump such inventory at dirt cheap prices. Another form of ROS inventory is inventory coming from some sections of publisher site which cannot be sold as premium inventory. For a newspaper site, such sections could include, job postings, obituaries, personals etc. Such sections have very low value for an advertiser and are thus given up as ROS inventory.
A lot of ad networks buy ROS inventory from publishers and try to make a profit by either reselling it or running direct response or branding campaigns on them. Such a collection of ROS inventory on an ad network is called Run of network (RON).
Typically ROS/RON inventory is prices quite cheap compared to premium inventory. As a result it is expected that it will perform poorly compared to premium inventory.





