The term is used to describe how well the electron cloud around an atom responds to changes in its electronic environment. A larger atom will hold its valence electrons tightly than a smaller atom and will therefore have a greater response to the presence of a charged or polar particle nearby.

polarizability, less

Explanation:

When any two ions of opposite charge and of different sizes approach each other closely, the cation tries to attracts the outermost electron of other ion and the result is called polarization.

Thus ,the ability of the cation to polarize the nearby anion is known as the  polarizing power of the cation.

It is the measurement of how comfortably or effortlessly the electron cloud gets distorted by an electric field.

The valence electrons of a large size atom is loosely bound and thus they are highly react to the presence of a polar particle or charged particle which lies nearby.