What is transformer coupling in amplifier?

A Transformer coupling is one in which the output stage of one amplifier is coupled to the input stage of next amplifier through a transformer. By choosing the appropriate turns ratio a transformer can be used to provide impedance matching with the load. If N1, N2 and Z1,Z2 are the turns ration and impedance of primary and secondary coil of the transformer then the primary coil impedance and secondary coil impedance are related as Z2 = Z1*(N2/N1)^2. Such coupling is used in high frequency amplification. Introduction of Transformer makes the amplifier bulkier and costly.