It means in both directions. A batting with those specifications probably won't hold up over time if you simply quilt straight lines 4" apart. The batting will likely start pulling apart at the quilting lines. You might be able to get away with lines 2" apart.
For what you would like to do, a batting such as Warm n Natural (quilting lines up to 10" apart) would work, and I'm sure there are Dream battings that would work too.