A delisted ad unit is an ad unit that has been removed from an ad network or platform. This can happen for a variety of reasons, such as if the ad unit violates the network's policies or if the advertiser has stopped using the ad unit.

When an ad unit is delisted, it is no longer eligible to be shown to users. This means that the ad will no longer be served by the network, and will no longer generate revenue for the advertiser or the publisher.

Delisting an ad unit can be a necessary step to ensure that the network's ad inventory is of high quality and compliant with the network's policies. However, it can also have negative consequences for the advertiser and the publisher, as it can reduce the availability of the ad and the potential revenue it can generate.