A domain is the human-readable name that stands in for a website's actual address, zeo.org rather than a string of numbers nobody could reasonably memorize. Every website ultimately lives at an IP address, and the Domain Name System, DNS, is what translates a typed domain name into that address behind the scenes every time someone visits.
Domains are structured hierarchically: a top-level domain (.com, .org, a ccTLD like .tr), a second-level domain (the "zeo" in zeo.org), and optionally subdomains stacked in front of that. Each registered domain is unique and can only point to one place at a time, though where exactly it points, and which subdomains or paths sit under it, is entirely up to whoever owns it. For SEO, the domain a business chooses becomes the foundation everything else builds on: backlinks, brand recognition, and search history all accumulate against that one address, which is part of why migrating to a new domain is treated as a high-risk move rather than a routine change.
