Answer:
The Poisson's ratio (ν) is a method to relate the longitudinal deformation of a material with its simultaneous lateral deformation.
Step-by-step explanation:
The Poisson's ratio (ν) is a method to relate the longitudinal deformation of a material with its simultaneous lateral deformation.
It can be expressed as

It is a measure of the Poisson effect, in which a material tend to expand in directions perpendicular to the direction of compression.