Barbara Feldman:

I got an email from an advertiser this morning who had a question about the definition of "run-of-site." He thought "run-of-site" meant that his ad would appear on every page load. Actually it means that an ad may appear anywhere on the site, without the advertiser getting to specify where.

While explaining this, I discovered MarketingTerms.com, which defines everything from "advertising network" to "under delivery." Oh, and their definition of "run-of-site" is here.