What does the non-active listing under my planet in the overview mean?

It means you are currently not building anything on that Planet, If you where building it would say what you where building and what level e.g - Metal Mine (15)

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Thnx anderson i know newb question especially considering (now that i think of it) i have seen the different building status' in the area in question.
Appreciate the help though

I actually asked the same question in another topic a few days ago
Just passing on the knowledge lol