Final answer:
The 'boundary' of our observable universe is called the visible horizon. We can only see objects within our observable universe, and anything beyond the visible horizon is beyond our reach of direct observation.
Step-by-step explanation:
The 'boundary' of our observable universe is called the visible horizon. It refers to the limit of our vision based on the idea that light has not had time to travel farther since the universe began.
This means that we can only see objects within our observable universe, and anything beyond the visible horizon is beyond our reach of direct observation.