Easton's Bible Dictionary: M. G. Easton, M.A., D.D.

Imputation

Is used to designate any action or word or thing as reckoned to a person. Thus in doctrinal language

1. the sin of Adam is imputed to all his descendants, i.e., it is reckoned as theirs, and they are dealt with therefore as guilty;
2. the righteousness of Christ is imputed to them that believe in him, or so attributed to them as to be considered their own; and
3. our sins are imputed to Christ, i.e., he assumed our "law-place," undertook to answer the demands of justice for our sins. In all these cases the nature of imputation is the same (Rom. 5:12-19; comp. Ph'm 1:18, 19).