the amplitude of the sinsuoid (its maximum value).
frequency
the frequency of the sinusoid in 0 to 2$\pi$ (number of cycles).
phase
the phase of the sinusoid (location of the peak).
...
additional arguments passed to the plot.
Details
Sinusoidal curves are very useful for modelling seasonal data. A sinusoid is plotted using the equation: $A\cos(ft-P), t=0,\ldots,2 \pi$, where $A$ is the amplitude, $f$ is the frequency, $t$ is time and $P$ is the phase.
References
Barnett, A.G., Dobson, A.J. (2010) Analysing Seasonal Health Data. Springer.