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.
This is called the Volts/Div. The figure following shows a sine wave with amplitude of 1 volt and the Volts/Div is set to 0.5 volts/division. (I am using a 4x10 grid for the display.) 1 In the following figure, the same sine wave is displayed; however, the Volts/Div is set to 1 volt/division.