Sine wave is the most single frequency of a signal, it is named because the waveform of this signal is a mathematical sinusoidal curve. Any complex signal,such as music signals, can be seen as a result of many different frequency, different sizes of sine wave composite.
Square wave is a non-sinusoidal waveform, usually in the electronic and signal processing occurs. Ideal square wave only has"high" and "low" these two values. High-level in a waveform cycle occupied by the time ratio is called the duty cycle, and the rectangular wave which has the duty cycle of 50% is called square wave.
