The Edit Curve defines the shape of the brush relative to the sculpting surface, separate from any alpha that is assigned to the brush.
To reduce the demands on your system when doing complex sculpting, ZBrush may use internally a slightly modified version of the Edit Curve defined in the user interface. This will not normally be noticeable. If you believe that sculpting is not showing all the details you’ve defined in the Edit Curve, turn on AccuCurve (Accurate Curve Mode). Alternatively, if you find sculpting slower than you’d like, trying turning AccuCurve off.
Values of WrapMode higher than 1 will allow multiple copies of a stroke to be applied to a model at the same time.
Wrap mode is normally best used with models that are symmetrical and simple in their rough form. A primary use is with planes, to permit quick production of tileable alphas. Since a single brush stroke can produce multiple strokes that preserve edge tileability, the amount of work is reduced.
Experimentation with sculpting a plane at different values of WrapMode is one of the best ways to understand it.
When the Curve By Pen button is activated ZBrush will use the Zero Curve as the modifier for the brush when the pressure is low and when the pressure is high ZBrush will transition into the Edit Curve to modify the brushs overall curve.
The Zero Curve will be applied to a brush when the Curve By Pen button is on and low pressure is being applied to the surface. When pressure is increased the curve that modifies the brush will be transfered to the Edit Curve.
The Pen Curve is the curve that sets the transition between the Edit Curve and Zero Curve when the Curve By Pen is active.