A course is a row of stitches which are yarn-wise adjacent. No stitch in a course uses a loop produced by another stitch in that course. Courses are transverse rows in a fabric. Every stitch in a course is created from the same set of active loops, often in a single carriage pass.
In single jersey, courses are the crosswise rows that appear on the back-side of the fabric.
Columns of stitches that are loop-wise adjacent are called wales. Wales and courses are perpendicular.