What is Vrect in a Voltage Regulator?
Vrect refers to the voltage drop of the rectifiers, such that they reduce Vpk by the amount Vdrop. The Vdrop depends on the diode used. Typical fast switching diodes have a forward drop of about 700 mV. Schottky diodes have a forward drop of about 500 mV.

Schottky diodes are used up to 24 VDC outputs, so they cannot be used for 48 or 100 volt outputs. They are more efficient at lower voltages but at voltages below 5 volts synchronous rectifiers are often used to get high efficiency.