The Catholic church addresses the concepts of serious and less serious sins. Catholics refer to this as mortal versus venial sins. The term comes from the Old French words venial, veniel or the Latin words venialis or venia, which means forgivable, permissible, pardonable, and something small. In contrast, a mortal sin is extremely serious, as "mortal" refers to something that kills.
Some criteria for committing a mortal sin are: it's serious, you know it's serious, but you do it anyways knowingly. Breaking some but not all of the Ten Commandments, like murder or adultery, are considered to be mortal sins. According to Catholic beliefs, mortal sins will send you to hell when you pass away. It is almost impossible to get right with God again. Venial sins, on the other hand, are minor and can be forgiven simply if one repents. Taking the Lord's name in vain would be considered a venial sin.
This may be a confusing matter as the seriousness of a sin is purely subjective. Often times, the context counts and so does the intention.
Venial as an adjective is used to describe something or someone who is worthy or admitting of pardon, forgiveness, or remission. It is not grave or heinous but instead, pardonable and light.
When considering venial sins, the first that many think of are white lies. There is no doubt that lying is wrong, but white lies are supposedly harmless, trivial and committed without the intention of hurting someone. In a sense, this is a venial sin because white lies are forgivable. One commits a venial sin when "in a less serious matter, he does not observe he standard prescribed by moral law" (Catechism of the Catholic Church 1862). If one does an immoral act and the act is not serious enough to be mortal, one is committing a venial sin. As an example, hatred can be a venial sin or a mortal sin depending on how strong that sense of hatred is. "Hatred of the neighbour is a sin when one deliberately wishes him evil. Hatred of the neighbour is a grave sin when one deliberately desires him grave him" (CCC 2303). However, even when a sin is enough to be considered seriously immoral, if the act is missing the essential elements of a mortal sin, the act is still considered venial. A venial sin is only committed when "he disobeys the moral law in grave, matter but without full knowledge or without complete consent" (CCC 1862).
Coarse language or cursing are other examples of venial sins. "Abusive language is forbidden by the fifth commandment, but would be a grave offence only as a result of circumstances or the offender's intention" (CCC 2073).
Although the term venial means forgivable, venial sins are still considered as inappropriate behaviour but will not result in a separation from God.
"venial, adj.1 and n.". OED Online. September 2012. Oxford University Press. 21 November 2012 <http://www.oed.com/view/Entry/222160?rskey=WjFoQl&result=1&isAdvanced=false>.