For something to be a “mortal sin” in Catholicism it has to be 1) a sin of grave matter, 2) there has to be knowledge that it is a sin and the person must 3) freely consent to the action. It is incorrect to throw around the phrase “mortal sin,” unless you are referring to a specific situation. Only God can fully know our hearts to discern definitively if something is a mortal sin, but it’s a good practice to bring things of grave matter into the Sacrament of Confession. There are many scenarios

What is mortal sin, and how do we know if we're committing a mortal sin? Chris Mueller, the Everyday Catholic, explains. New episodes every Thursday! | EWTN