When can there be many Waves in a context on Google Wave

In a Google Wave Robot, the event handler gets a Context object.

One of the methods is GetWaves, that is documented as:

"""Returns the list of waves associated with this session."""

I am trying to understand when this would return more than one Wave.

What are the situations where there is more than one Wave associated with the session/context?

I haven't looked at the API, so I'm just guessing based on the UI that I see. I'd assume session here is a login session. I have 4 different waves open in my browser, which I'd assume is associated with a single session. Would that explain it?