An offense against God which does not deprive the sinner of sanctifying grace. It is called venial (from venia, pardon) because the soul still has the vital principle that allows a cure from within, similar to the healing of a sick or diseased whose source of animation (the soul) is still present to restore the ailing bodily function to health.
Deliberate venial sin is a desease that slackens the spiritual powers, lowers one's resistance to evil, and causes one to deviate from the path that leads to heavenly glory. Variously called "daily sins" or "light sins" or "lesser sins," they are committed under a variety of conditions: when a person transgresses with full or partial knowledge and consent to a divine law that does not ablige seriously; when one violates a law that obliges gravely but either one's knowledge or consent is not complete; or when one disobeys what is an objectively grave precept but due to invincible ignorance a person things the obligation is not serious.
The essence of venial sin consists in a certain disorder but does not imply complete aversion from humanity's final destiny. It is an illness of the soul rather than its supernatural death. When people commit a venial sin, they do not decisively set themselves on turning away from God, but from overfondness for some created good fall short of God. They are like person who loiter without leaving the way.