The area where there is neither compression nor tension during bending.
The trace of that plane in a beam where there is no tension or compression and where no deformation takes place.
The plane through a member (at the geometric center of the section in symmetrical members) where the fibers are neither under tensile nor compressive stress during bending.
Centroidal axis, transverse to longitudinal axis of a structural member, which is neither stretched nor shortened by bending of the member.
An axis in the cross section of a beam, shaft or the like along which there are no longitudinal stresses / strains.