radius of gyration
The radial distance from any axis to a point at which the mass of a body could be concentrated without altering the moment of intertia of the body about that axis. For a structural section, the radius of gyration is equal to the square root of the quotient of the moment of intertia and the area. The higher the radius of gyration of a structural section, the more resistant the section is to buckling. In determining the cross-sectional shape of a column, the objective is to provide the necessary radius of gyration about the different axes. For an asymmetrical cross section, buckling will tend to occur about the weaker axis or in the direction of the least dimension. (Ching, 1995)