An Urbit ID is a decentralised addressing and public key infrastructure for the Urbit operating system. Addresses are connected to NFTs on the Ethereum blockchain and these IDs are all composed of four syllables, such as ~digsev-hocfex.
You are able to search for a user within Urbit using their ID and attempt to interact with this person. If you are wanting to chat, for example, you can search for ~digsev-hocfex and request to chat. In addition to talking with others online, you can share content and send value to the user (such as Bitcoin).
Every Urbit ID has an associated sigil, which is an image composed of four parts that corresponds to the sounds of user’s ID name. These symbols are used in many combinations to create the 4.3 billion accounts (ships) on the Urbit network.
The Urbit user owns their ID indefinitely. There are no ongoing fees – once you own an ID, it is yours forever (don’t lose your key, though, or it will be unusable forever).