The phase of a simple harmonic oscillation or sinusoidal signal is the value of φ φ in the following functions: x ( t ) = A cos ⁡ ⁡ ( 2 π π f t + φ φ ) y ( t ) = A sin ⁡ ⁡ ( 2 π π f t + φ φ ) = A cos ⁡ ⁡ ( 2 π π f t + φ φ − − π π 2 ) where A , f , and φ φ are constant parameters called the amplitude, frequency, and phase of the sinusoid. These signals are periodic with period T = 1 f , and they are identical except for a displacement of T 4 along the t axis. The term phase can refer to several different things: