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. Philemon 1:18, 19)." 
Imputation is distinct from impartation and infusion. The Greek verb for imputation, logizomai is used more than 40 times in the New Testament. It used ten times in Romans chapter 4—sometimes called the "imputation chapter."
In the King James Version, logizomai is translated 'counted' (Rom 4:3, 5), 'reckoned' (Rom 4:4, 10), and 'imputed' (Rom 4:6, 8, 11, 22, 23, 24).