To my knowledge, there is no such distinction between observing an interface and interacting with an interface as terms officially used by UX professionals. The reason for that can be debated, but the real use for distinction between observation and interaction could be that there are no such test done where you let a user just observe an interface and not let her interact with it.
Still, the process of observing and interacting with an interface is called functional prototyping. This means that the tester is “observing people as they use a very simple website or application prototype that has copy in place”. This would do on a live real web site as well – and the tester writes down (or does a video recording) of the users experience during a task.
The observations is often the input to “wire frames, user flows, the use case / requirements document, the UI design and the content”.
Reference: A List Apart “Can You Say That in English? Explaining UX Research to Clients”