Quadrature Amplitude Modulation (QAM) is a sophisticated modulation technique used in telecommunications and broadcasting to transmit data efficiently. It involves combining two separate signals, each modulated by varying their amplitude, into a single channel. This is achieved by using two carrier waves that are out of phase with each other by 90 degrees, known as being in quadrature. By modulating these two carriers independently, QAM effectively doubles the amount of data that can be transmitted over the same bandwidth compared to traditional amplitude modulation methods.

In practice, QAM is widely used in digital television, cable modems, and wireless communication systems, such as Wi-Fi and cellular networks. The technique allows for higher data rates and improved spectral efficiency, making it a crucial component in modern communication systems. Different levels of QAM, such as 16-QAM, 64-QAM, and 256-QAM, indicate the number of different amplitude and phase combinations used, with higher levels allowing for more data to be transmitted but requiring better signal quality to maintain accuracy.