Today job grading is mainly used as a synonym for analytical job evlaluation with a point-factor comparison. The resulting grade shows the relative value of the positions.
Before the greater distribution of analytical job evaluation systems "job grading" sometimes was used to describe a non analytical method of "job ranking". See: Johannsen, Page (1980), p.184
Occasionally job grading is used to describe the method of performance appraisal of a position holder, as in Sutherland / Canwell (2004),