What is a Blockstack Subdomain

This is also a Blockstack ID, and can be used for all the things a Blockstack ID can be used for. The only difference is that they have the format foo.bar.baz instead of bar.baz. For example, jude.personal.id is a Blockstack ID, and is a subdomain of personal.id. Subdomains are first-class Blockstack IDs---they can be used for all the same things that an on-chain Blockstack ID can be used for, and they have all of the same safety properties. They are globally unique, they are strongly owned by a private key, and they are human-readable.Subdomains are considerably cheaper than Blockstack IDs, since hundreds of them can be registered with a single transaction. The [BNS documentation]({{ site.baseurl }}/core/naming/introduction.html) describes them in detail. Subdomains provide a fast, inexpensive way to onboard many users at once.