What is fqn attribute in LightningComponentBundle?

What is the fqn attribute in the LightningComponentBundle element? I can’t find it documented anywhere. Is this the unique identifier by which Salesforce manages the element? Would that be the identifier used in the members element in package.xml? If I change it, does that change the "identity" of the component, so SF no longer thinks it’s the same one?

See the example at https://developer.salesforce.com/docs/component-library/documentation/en/lwc/lwc.use_config_for_community_builder, which contains the line

<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata" fqn="helloWorld">