Uncover a father’s skirt / wing
Here’s what it means
To violate the father's marital rights by sexual relations with his wife.
Why the Bible says it this way
The garment stands for the man's marriage authority and household relationship.
The Bible sometimes uses gentler words for a private or sensitive subject.
A helpful detail: Ruth 3:9 uses related 'wing/garment' language positively as a marriage-protection request, not as violation.