1. A method for defect classification comprising: storing, by a computer system, a plurality of definitions of a plurality of defect classes in terms of a plurality of classification rules in a multi-dimensional feature space; receiving, by the computer system, inspection data associated with a plurality of defects detected in one or more samples under inspection; generating, by the computer system, a plurality of first classification results by applying an automatic classifier to the inspection data based on the plurality of definitions, wherein the plurality of first classification results comprise a class label and a corresponding confidence level for a defect of the plurality of defects; upon determining that a confidence level for a defect is below a predetermined confidence threshold, generating, by the computer system, a plurality of second classification results by applying at least one inspection modality to the defect; and generating, by the computer system, a report comprising a distribution of the plurality of defects among the plurality of defect classes by combining the plurality of first classification results and the plurality of second classification results.