phrases - What's the meaning of "out" in "build out"?

From NPR

Critics suggest these big ISPs aren't building out their networks enough to keep pace with the huge growth in demand.

I haven't found the definition of "build out" in the dictionary, so I looked "out" up, and find the following definition:

out: used to say that something is done carefully or completely

And examples about the usage:

I spent all morning cleaning out the kitchen cupboards.

In the summer months the soil dries out quickly.

I want to know if "out" fit in with the definition. And I guess "build out" means "build carefully and completely", doesn't it? Because I have encountered the expression twice, I want to know the exact meaning, but I cannot find it on the Internet or dictionary.

Answer

That's an interesting phrase.

"Building out" in this sense probably means growing, spreading out.

And I guess "build out" means "build carefully and completely", doesn't it?

I don't think so, although it could. Given the context, it sounds like internet providers are trying to expand their properties to compete, and not necessarily to finish a specific project or directive. It just looks like a conjoining of "building" and "spreading out". If I were talking about a project, although it would sound extremely unusual, I could say "We're about to build out that particular phase", and the person I was talking to could probably get the idea, although I would much more likely say "We're about to finish out that particular phase" or "complete".