Incentivized traffic is traffic from websites, platforms or apps where visitors get rewarded for simply visiting the website or performing any actions on it (e.g. completing surveys, clicking links, etc.).
There are various models for incentivised traffic, e.g. monetary rewards for visiting a website. Another example are gaming sites which will give out non-monetary rewards, e.g. a bonus or a boost for the game for returning customers.
While some advertisers find such traffic beneficial, others do not as the conversion rates of such traffic are generally lower.
This is why on AdEx you are able to exclude incentivized traffic from your campaign audience when creating an advertising campaign.
Please note that the CPM for incentivised traffic will be lower so you can take advantage of it if you'd like to reach a wider audience with a smaller budget.