Sitecore multisite means running several websites from one Sitecore instance. Brands, regions or languages can have their own sites while sharing content, components and governance.
This reduces duplicate effort. Teams reuse layouts and templates, and new sites can launch faster than a separate build each time. Permissions let each site team manage its own content.
Tools such as SXA are often used to set up multiple sites in a consistent way.
Regal Rexnord built new brand sites faster. Read the case study.