What is the difference?
What is the difference between: 시아버지 and 장인어른?
And what is the difference between: 시어머니 and 장모님?

Question

What is the difference?
What is the difference between: 시아버지 and 장인어른?
And what is the difference between: 시어머니  and 장모님?

Answer

"시아버지" and "시어머니" are the parents in law for the bride.
"장인어른" and "장모님" are the parents in law for the groom. :)