A set that is not convex is called a non-convex set. A polygon that is not a convex polygon is sometimes called a concave polygon, and some sources more generally use the term concave set to mean a non-convex set, but most authorities prohibit this usage.
In either case you don't need to deal with the absolute value. A rectified sine wave is a periodic signal with a period equal to half of the full sinusoid, I would write the sine in exponential form and integrate over one period to find the series coefficients.
A sinusoidal curve is the graph of the sine function in trigonometry. A sinusoid is the name given to any curve that can be written in the form. The example at the right is. The cosine wave is also said to be sinusoidal because of the relationship which makes it the sine wave with a horizontal shift.