Re-direct 
The process of a server sending a browser the location of a requested ad, rather than sending the ad itself.

Referral
A new member of a network referred by a current member.

Revenue share
Pricing model where advertisers pay publishers a percentage of the revenue earned.

Rich media
Method of communication that incorporates animation, sound, video, and/or interactivity; can be used either singularly or in combination with the following technologies: streaming media, sound, Flash, and with programming languages such as Java, Javascript, and DHTML. (Source: IAB)

ROI (Return on Investment)
Net profit divided by investment - a metric that attempts to determine what the advertiser receives in return for the cost of the advertising.

RON (Run of Network)
Scheduling of Internet advertising whereby an ad network positions ads across the sites it represents at its own discretion, according to available inventory. (Source: IAB)

ROS (Run of Site)
Scheduling of Internet advertising whereby ads run across an entire site, often at a lower cost to the advertiser than the purchase of specific site sub-sections (Source: IAB)