The phrase "axial direction" refers to the line or path that runs straight and parallel to an axis, which is an imaginary line or central point of reference. It basically means the direction or orientation along the axis. Full definition
As explained in the research paper, the resolution approaches the angstrom scale only in the axial direction, where it is estimated at 0.6 nm. (foresight.org)
While STED can overcome the diffraction barrier down to 5 nm in the lateral direction, 4Pi Microscopy can increase the resolution in the axial direction by using two opposing lenses. (ulrikeboehm.org)
Both motors utilize segment conductor winding, where the coil is inserted from the axial direction of the stator core, providing a denser and more compact stator than the previous motors» distributed winding arrangement, where the coil is inserted from inside the state core. (greencarcongress.com)