The English term 'rectification' has several different meanings:
1: The conversion of alternating current to direct current
2: determination of the length of a curve; finding a straight line equal in length to a given curve
3: the act of offering an improvement to replace a mistake; setting right
4: (chemistry) the process of refinement or purification of a substance by distillation
Basically it takes an AC or modified DC and attempts to smooth or change it. Diodes will clip (block) one side of the AC, caps will help smoothing as well. Hard to explain without pictures. But look up power supplies and rectifiers in google. Will be plenty on bridge rectifiers and smoothing.