I'm calling it a Straight Line Stipple.
Add dimension by changing the line of stitching, creating open boxes here and there. Notice there's no crossing over on any of the lines - this is a geometric take on the traditional stipple. And don't worry about maintaining an exact distance between the lines. As long as the overall density stays consistent, it will look great!
For my place mat project, the space between lines is anywhere from 1/8" to 1/2". For a larger space to fill, the spacing could be somewhere between
1 1/2" to 3". It's all up to what the quilt (and quilter) want.
Here's a video to see the Straight Line Stipple being stitched, using backtracking within the ditch to move through the space.
Quite a fun, easy, modern fill, suitable for a domestic or longarm machine, and perfect for a variety of quilts. Enjoy!