A subregistry is a contract on your name that manages the names underneath it. You need one before you can create subnames.

The ENS registry is the single shared contract that records, for every ENS name, who owns it and which resolver it uses. It's canonical and global.

A subregistry is a contract deployed on one specific name to handle that name's subnames. Think of the registry as the main phone book and a subregistry as a smaller one you run for names under yours.

In practice: you read the registry to find who owns yourname.eth; you read the subregistry on yourname.eth to find who owns alice.yourname.eth. The registry always tells you which subregistry, if any, governs a name's subnames.

Because your subnames then live in your contract rather than directly in the shared registry. That lets you set your own rules — who can claim a subname, whether it expires, how it's issued — without affecting the rest of ENS.

If you don't want subnames, you don't need a subregistry. Leave it undeployed.

Deploying a subregistry is the first step of creating a subname. See Create a subname.

The Registry tab. It shows the registry the name lives in, the subregistry if one has been deployed, and the parent registry above it.

The overview row can lag behind. The Registry tab is the one to trust — if it shows the subregistry, the deployment worked.