Spacing is a method used to place blank space between the text to space it out further than normal. This is a scale factor as it is not in inches or mm's, but is instead a scale of how far the letters are from each other compared to their normal values.
This is not a very common item to change, as it can make the text harder to read, but it is a feature that may at some point be useful.
You can set the spacing to any value from 0.75 - 4.00 as the scale factor in the spacing.
For instance using the normal value of 1.00 and then 2.00 would yield the following result.