Interface

doc
1

An interface is a topology provided by the juju controller to enable information sharing between units of different applications.

An endpoint is specified a charm’s metadata.yaml for a corresponding interface. A charm can provide or require an endpoint for operation. Endpoints are used when integrating 2 applications. Note: peer integrations happen automatically and do not need to be specified with the juju integrate command.

3

I suggest this doc for charm authors.

The juju relate/integrate help page refers to endpoints.

4

Looking at the operator framework docs, they do not use the work interface in relation to relations. The word is so far only used in metadata.yaml as a tag.