In Huddleforce Applications, you can create properties so that users can assign a personalized value. 

When a family subscribes to an application in the Marketplace, they will be prompted to enter a text answer.

A use case might be if a Huddleforce Application was built to collect data from an external API source where that source required an API to identify accounts on their system.  In Huddleforce, each subscribing family would be able to enter a unique API Key so that when the application rendered under their Huddleforce login credentials, the API key they entered when subscribing could be accessed by your application and passed into the external API request.

Property values entered by the subscribing user are stored in a runtime property collection for the application that can be referenced in Javascript like this:

var aSettings = ApplicationRuntimeSettings('d78876ff-cbdb-4786-bbf3-0264c4937d11');


// if additional application properties were created, you can access them this way:
// aSettings.PropertyValues[1].Key
// aSettings.PropertyValues[1].Value

See this article on how to obtain all Huddleforce Session Properties