What is the meaning of Sister-in-law?

A female relative of one's generation, separated by one degree of marriage:

1. The sister of one's spouse.

   The sister of one's spouse.

   The wife of one's sibling.

   Co-sister-in-law: The wife of one's sibling-in-law.

   1. The wife of the sibling of one's spouse.
   2. The sister of the spouse of one's sibling.

   The wife of the sibling of one's spouse.

   The sister of the spouse of one's sibling.

   Source: wiktionary.org