A subdomain is a subdivision of a main domain name, created by adding a specific extension before it, as in forum.my-domain.com. It allows you to structure a website into distinct and independent sections without requiring an additional registration process. Subdomain management is generally handled through the interface of the main domain’s hosting provider, often free of charge. They can be used to optimize online visibility by integrating keywords into the URL and to distribute the load on servers during traffic spikes, although their impact on organic search engine optimization (SEO), particularly on Google, is decreasing.