Whois was an online search tool to discover the contact information of a domain name registrant -- see ICAAN Whois search, and was provided by many domain name registrars.
Many businesses rely on Whois searches to identify intellectual property infringers. As we approached May 25, commentators predicted that the Whois service would be effectively neutered because of the EU General Data Protection Regulation (GDPR).
Generally, they are correct.
Some registrars are no longer collecting certain personal data concerning the registrant, and some registrars are redacted all personal data concerning domain name registrants. If information is no longer collected or only produced in redacted form, then the utility of the Whois service has been eviscerated.
However, there is still hope to identify website owners. GoDaddy has taken the position that it will only redact the personal data for persons with an address in the EU (see link). And for websites that are subject to the GDPR, the GDPR requires that they identify the contact details for the entity running the website (Art. 13(1)(a)).