Site sections let site-targeted campaigns target a specific section or page of a website

Site targeting gained the option to target a section or individual page of a site rather than the whole domain, so ads could appear only where the content was relevant. Sections could be added when creating a site-targeted campaign or through the Edit Sites and CPMs link.

Google's post says the feature had been released the previous week; the timeline dates it October 11, 2005 and the post is dated October 12.