An install reference is a randomized identifier issued to each app installation, used to recognize a device without tying it to a person's real identity. It is how the proximity method keeps presence private by design.
The longer version
An install reference is generated per app instance. When the app is installed, it receives a random reference that the system uses to recognize that installation. The reference identifies the install, not the human behind it.
This is a privacy by design choice. Because the presence layer works with a randomized install reference rather than a name, phone number, or account, the system can resolve who is nearest without exposing personal identity in the process.
The install reference pairs with server routing to keep control on the person's side. The server can match the nearest install and prepare a transaction, while the sensitive account details stay with the server and nothing is sent until the user acts.
The Parousya method
Install reference is Parousya's own term for how the method identifies a device. It is a randomized reference tied to an app install rather than to a person, which is what makes presence detection private by design.