Both the ladder stitch and square stitch looks very similar; virtually identical. But they are not.
Generally, you will see the ladder stitch as but one row. Though they can be more than one row (I think).
The Square Stitch is also known as Box Stitch.
Both the ladder and square stitch resembles loomwork and can be used in lieu of (for small pieces of work).
Closer Look at Ladder vs Square Stitch