Visitors who have received some form of compensation for visiting a site.
The danger of incentivized traffic is when 3rd-party promoters compensate people for visiting your site without disclosing that information to you. Incentivized traffic is widely regarded as of a much lower quality than unincentivized traffic. Incentivized visitors typically do only what is necessary to gain the incentive and nothing more.
Incentives may come in the form of cash, points, or other means. While incentivized clicks/traffic is the most notable incentive-based action, other forms exist such as incentivized registrations.
Incentive Sites: Love Them or Leave Them
ClickZ (May 18, 2001)
Beware the Dot-Com Tollbooth
ClickZ (September 6, 2000)