What are "Proxies for ad verification"?

Selling proxies for ad verification; what does this mean?

I've read this as a feature on some proxy sellers websites. Does this mean they are advertising proxies that are not detected by anti-click fraud tools like "click cease"? So that advertisers can check ads running?

The online ad market is prone to fraudulent activities from hackers who use ads to drive traffic to their page. If you provide an ad service, then you’ll have to use the best proxies to aid in the ad verification process.
Ad verification is basically the process undertaken by ad verification companies to make sure that the ads placed online are placed properly on a real site and viewable by all visitors.
A proxy serves as the doorway between the user and the website. If you want to visit a particular website, the proxy will send this request to the proxy server first.