Known sin

חטא הידוע

It is called the known sin because there is a reluctance to detail the sin involved 

Shiurim in this topic
3618. Surely you should study Chitas on Shabbat. We also recite Tehillim on Shabbat.
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3651. You should rule leniently in situations where a woman is afraid of becoming pregnant.
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3769. Transformation Through Contemplative Fasting: A Chassidic Teaching
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