GDPR (General Data Protection Regulation) is regulation from the European Union regarding how marketing information can be collected and shared.
When you go to a website, and you get a popup about accepting all cookies, or only the required ones? That is a GDPR requirement. If you have ever joined a newsletter mailing list, and been required to verify your subscription, this is also a GDPR requirement. GDPR non-compliance can have hefty fines (such as 20 million euros, or 4% of your revenue), even for those outside the EU.