Axis is the orientation of the cylinder portion of your lens prescription, used to compensate for astigmatism. You don't have an axis value if you don't have astigmatism. From the lens wearer's perspective, 0 degrees of axis is horizontal, and increasing values move clockwise around the eye. The axis of cylinder is symmetrical, so it only goes from 0 to 180 degrees.
Axis of astigmatism can be measured with a stenopaeic slit or JCC lens but the use of these tools is complex and easily misunderstood, it's usually best to get your axis off of your most recent prescription.