Being spammed with unsolicited ads becomes causes multiple problems: mailboxes are overloaded, network traffic increases, waste of time to delete / unsubscribe from all these unsolicited senders or spammers, important messages may be lost in the mass of spam. Therefore advertisement blockers become useful and popular.
Pi-hole, available under the European Union Public Licence (EUPL) is a very popular ad blocker that works on Linux servers independently of web browsers. It blocks advertising across the network by redirecting the servers from which the advertising or other unwanted content comes, at the DNS level. Because Pi-hole is DNS-based, it can also serve as a private DNS server. Pi-hole requires minimal resources and can easily run on small computers like the Raspberry Pi. It can also be installed on other Linux systems or operated as a Docker container.
Designed for Linux-driven server hardware, Pi-hole aim is to protect devices from unwanted content, without installing any client-side software.
Pi-hole development team focuses on the easy-to-install aspects, on blocking content in non-browser locations such as ad-laden mobile apps and smart TVs, on being Lightweight (running smoothly with minimal hardware and software requirements), on working on both IPv4 and IPv6 and being capable of handling hundreds of millions of queries when installed on server-grade hardware.
More information: https://pi-hole.net/