Rashi on Leviticus 18:23/רש"י על ויקרא י״ח:כ״ג

1תבל הוא THIS IS CONFUSION — תבל is an expression used for unchastity, incest and adultery. Similar is (Jeremiah 10:25) “Mine anger because of their depravity (תבליתם)". Another explanation of תבל הוא: it is an expression denoting the mingling (root בלל) and fusion of the human seed and the animal seed.