Impedance: Impedance is the measure of the opposition to the flow of a signal, such as electrical current or sound waves, through a medium.
Characteristic Impedance: Characteristic impedance is the ratio of the pressure to the volume velocity of a sound wave in a medium, which is a constant value determined by the properties of the medium.
Reflection Coefficient: The reflection coefficient is the ratio of the reflected sound wave amplitude to the incident sound wave amplitude, which is determined by the difference in acoustic impedance between two media.