Poison’s ratio is the ratio of lateral strain to longitudinal strain. It is the property of elasticity of a material.

This means that, if a force is applied in a given direction, say along the axis of the member, then the poison’s ratio is the ratio of the strain in the direction perpendicular to the axis and the strain along the axis.

The poison’s ratio of concrete is 0.1 to 0.2. Let’s take that it as 0.15. If a force is applied on a concrete specimen along its axis, then, for every 1 unit of deformation in the axis, 0.15 unit of deformation happens in the perpendicular direction.

Poison’s ratio is a measure of the elastic property of a material. There isn’t any direct relation between the strength of the material and the poison’s ratio.