Sin Be Holy Like our Father in Heaven is Holy and Sin No More

In Catholicism, sin is defined as an offense against reason, truth, and right conscience. It is an intentional thought, word, deed, or omission contrary to God's eternal law. More than just breaking arbitrary rules, sin is viewed as a failure in genuine love for God and others, which fractures relationships and damages the human soul. [1, 2, 3]

The Catholic Church categorizes sin into two primary types depending on its severity:

Mortal Sin

• Definition: A grave violation of God's law that turns a person completely away from God.
• Three Conditions: To be considered mortal, the act must involve grave matter (serious offense, such as murder or adultery), be committed with full knowledge that the act is sinful, and require full consent of the will.
• Effect: It destroys the life of grace (charity) within the soul. If left unabsolved, it separates a person from God for eternity.
• Remedy: It requires the Sacrament of Reconciliation (Confession) to be forgiven. [1, 2, 3, 4]
Venial Sin
• Definition: A less serious offense or a failure to follow the moral law in a lighter matter.
• Effect: It weakens one's relationship with God but does not destroy the divine life within the soul or entirely cut the sinner off from God's grace.
• Remedy: These can be forgiven through sincere repentance, prayer, acts of charity, and receiving the Eucharist, though regular confession is highly encouraged. [1, 2, 3, 4, 5]
The Root of Sin
Catholic teaching also recognizes Original Sin, which is the foundational state of human nature inherited from Adam and Eve. It describes a "fallen" condition where human beings are naturally inclined toward selfishness and struggle to choose God's will. [1, 2, 3, 4, 5]
To explore the exact teachings and specific moral guidelines, you can read the full section on sin in the Catechism of the Catholic Church or learn more about the theological concept on Catholic Answers.

Catechism Part Three Section One Man's Vocation Life In The Spirit Chapter One The Dignity Of The Human Person Article 8 Sin II. The Definition Of Sin

II. The Definition of Sin 

https://www.vatican.va/content/catechism/en/part_three/section_one/chapter_one/article_8/ii_the_definition_of_sin.html

1849 Sin is an offense against reason, truth, and right conscience; it is failure in genuine love for God and neighbor caused by a perverse attachment to certain goods. It wounds the nature of man and injures human solidarity. It has been defined as "an utterance, a deed, or a desire contrary to the eternal law."¹²¹

1850 Sin is an offense against God: "Against you, you alone, have I sinned, and done that which is evil in your sight."¹²² Sin sets itself against God's love for us and turns our hearts away from it. Like the first sin, it is disobedience, a revolt against God through the will to become "like gods,"¹²³ knowing and determining good and evil. Sin is thus "love of oneself even to contempt of God."¹²⁴ In this proud self-exaltation, sin is diametrically opposed to the obedience of Jesus, which achieves our salvation.¹²⁵

1851 It is precisely in the Passion, when the mercy of Christ is about to vanquish it, that sin most clearly manifests its violence and its many forms: unbelief, murderous hatred, shunning and mockery by the leaders and the people, Pilate's cowardice and the cruelty of the soldiers, Judas' betrayal - so bitter to Jesus, Peter's denial and the disciples' flight. However, at the very hour of darkness, the hour of the prince of this world,¹²⁶ The sacrifice of Christ secretly becomes the source from which the forgiveness of our sins will pour forth inexhaustibly.

Be Holy Like our Father in Heaven is Holy and Sin No More

https://www.vatican.va/content/catechism/en/part_three/section_one/chapter_one/article_8/ii_the_definition_of_sin.html