What is the file path name on mac?

The samples you show are both pathnames of a particular FILE.

To specify 'where to save', just as iSystem suggests, you would generally omit the actual filename, which leaves the pathname of a DIRECTORY, where your file (any name) can be saved.

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Almost all Mac Applications use a standard dialog-box, which CAN allow you to specify the save-location easily. The default looks like this, which is extremely limited:

when you click the discloser triangle to the right of the proposed filename, the controls, including drop-down boxes (this one wants to save in the "screen shots" folder) appear:

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May I have the screenshot showing the required input for the path?

For the programs that I use, such as Lightroom, I simply enter the format as /Users/bd/Documents/Thesis/Thesis/ Data/20171125/OMS.sav

Also, depending on the application, you may also want to omit OMS.sav if the file is yet to be created.

well that changes things a bit.

The first extra \ you are seeing is to escape the trailing space character from "Thesis Data", so that it will not be parsed as a separate token. If you change the "Thesis Data" directory name to ThesisData or Thesis_ Data, that extra escape complexity would disappear. Or you can use quotes as I did above.

You may have a directory or filename reference that starts with a blank character messing things up. I think I see an extra \ character, not sure.