to zero in

to focus attention: We need to zero in on the client’s exact expectations for this software. Don’t bother with any additional functionality at this stage.

to zip up 

to keep something quiet: Keep this matter zipped up will you? It’s still highly confidential.

to zoom in

to magnify an image: Can you zoom in on that part of the picture? I want to read what the poster says.

to focus attention: Let’s now zoom in on the company’s debt problem.