# Ad blocker

> Browser software that blocks ads and, often, the tracking scripts and pixels that measure them.

Source: https://datacenter.so/glossary/ad-blocker
Also called: content blocker, tracker blocker.

Ad blockers and privacy browsers use filter lists to stop requests to known ad and tracking addresses. Many lists include analytics and ad pixel domains, so the visit happens but the tool never hears about it.

Effects on your data:

- Analytics tools on blocked domains undercount visitors and conversions.
- Ad pixels miss conversions, so ad platforms see fewer sales than happened.
- Two tools can disagree because one is blocked more often than the other.

To see the size of the effect on your own site, the free [ad blocker estimator](https://datacenter.so/tools/ad-blocker-estimator) shows the math with your numbers, and running two tools side by side for a week gives you the real gap.

Measurements that do not depend on the browser are not affected: orders read from your store, payments from your payment processor, and conversions sent from your server. See [server-side vs client-side tracking](https://datacenter.so/guides/server-side-vs-client-side-tracking).

## Related terms

- https://datacenter.so/glossary/server-side-tracking
- https://datacenter.so/glossary/bot-traffic
- https://datacenter.so/glossary/itp