Permeability can be defined as the property of a membrane to allow transport of a given substance across it.
It depends on:
The size of pores in the plasma membrane
The size and charge of the molecules of the given substance
Based on the permeability, the membranes can be of following types:
Permeable membranes: If a given substance passes readily across the membrane.
Impermeable membranes: If a given substance cannot pass through the membrane.
Semipermeable membranes: If the membrane allows only water molecules to pass through it and solutes and not allowed at all.
Selectively permeable membranes: If the membranes allow some selected solute molecules to pass through it along with water molecules. These are also called differentially permeable membranes. Such membranes operate in the biological systems.
Note:
The semipermeable membranes are used for the operation of osmosis.
The selectively permeable membranes are used for the operation of diffusion.