A subdomain is a name nested under a parent domain, typically separated by a dot-for example, help.example.com under example.com. Organizations use subdomains to separate services or websites. Hosting platforms can make them easy to create in large numbers.
In cyber security, subdomains can be used for legitimate services or abused to host disposable scam pages, phishing content, or redirect layers. Attackers may use many subdomains to make fraudulent pages appear separate or to replace them quickly. Defenders should assess the page and its surrounding infrastructure, not assume a hosted subdomain is trustworthy because it belongs to a familiar platform. Monitoring for suspicious patterns and reporting abuse to the hosting provider can help limit harm.