Цитата из https://www.allaboutcookies.org/manage-cookies/opt-out-cooki... с описанием сабжа:
What is an Opt-Out cookie?
Opt-out cookies are cookies created by a website on your browser folder that enables you to block that same website from installing future cookies. The opt-out cookie tells the website not to install third party advertiser or other cookies on your browser. This prevents the third party ad server from tracking your page preferences within a website or among websites within their network.
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These are essentially cookies used to avoid cookies. Accepting an opt-out cookie blocks future cookies being installed on your browser by a particular website server or advertiser.
Имхо, "блокирующие" передает их назначение