$K$ is $L$ 's wife and $M$ is $L$ 's sister. $N$ is the daughter of $K$, while $O$ is $M$ 's mother. What is the relation of $O$ to $K$?

Let's break down the relations step-by-step:
1. $K$ is the wife of $L$. This means $L$ is a male (husband) and $K$ is a female (wife).
2. $M$ is $L$ 's sister.
3. $O$ is $M$ 's mother. Since $M$ and $L$ are siblings, $O$ must also be the mother of $L$.
4. Now we need to find how $O$ relates to $K$: $O$ is the mother of $K$ 's husband ($L$).

The mother of one's husband is called a Mother-in-law.