Disavow.

Google introduced the disavow tool in 2012, at a time when many websites had accumulated bought or artificially created links and Google had begun penalising such link patterns. The tool was meant to give site owners a way to distance themselves from links they could not have removed. The name comes from the English 'to disavow', to renounce something.

Technically the procedure is simple: you create a text file in which each line contains either a single URL or a whole domain with the prefix 'domain:', and upload it in Search Console for the relevant property. Google takes the list into account in later crawls, so the effect is not immediate. A new file completely replaces the old one.

Google stresses that most websites never need the tool. Today Google largely recognises low-quality links itself and ignores them instead of downgrading the target website for them. Spam links from dubious sites that appear without any action on your part are normal and no cause for concern. A wrongly used disavow can do harm, though, if valuable links are devalued by mistake.

Disavow makes sense mainly in two situations: when Google reports a manual action for unnatural links in Search Console, or when it is known that links were bought or exchanged on a larger scale in the past, for example by a previous agency, and these links can no longer be removed.