Catechism of the Catholic Church 2515
Etymologically, “concupiscence” can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of the human reason. The apostle St. Paul identifies it with the rebellion of the “flesh” against the “spirit.” ( Cf. Gal 5:16,17,24; Eph 2:3). Concupiscence stems from the disobedience of the first sin. It unsettles man’s moral faculties and, without being in itself an offense, inclines man to commit sins (Cf. Gen 3:11; Council of Trent: DS 1515).