It is a quantity derived from a cross-section (similarly to the more well-known moment of inertia of an area Iy and Iz). The warping constant is required, among other things, for the determination of stresses for the warping torsion as well as for the determination of critical buckling moments for the lateral-torsional buckling analysis.
Users of the Dlubal Software programs can use the "Info About Cross-Section..." function at any time to open the corresponding cross-section properties, including the warping constant.