die Schwägerin
sister-in-law
The sister of one's husband or wife.
Meine Schwägerin, die Schwester meines Mannes, kommt am Wochenende zu Besuch.
My sister-in-law, my husband's sister, is coming to visit this weekend.

sister-in-law
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sister-in-law
The sister of one's husband or wife.
Meine Schwägerin, die Schwester meines Mannes, kommt am Wochenende zu Besuch.
My sister-in-law, my husband's sister, is coming to visit this weekend.

Since the word can describe two different family relationships, Germans often add an explanation in conversation to avoid misunderstandings. For example, say 'meine Schwägerin, die Frau meines Bruders' (my sister-in-law, my brother's wife).
Ich fahre am Wochenende zu meiner Schwägerin, der Schwester meiner Frau.
I'm driving to my sister-in-law's this weekend, my wife's sister.
The relationship is reciprocal. If your brother's wife is your 'Schwägerin' (sister-in-law), then you are also her 'Schwägerin' (sister-in-law) if you are a woman, or her 'Schwager' (brother-in-law) if you are a man.
Meine Frau und ihre Schwester sind Schwägerinnen.
My wife and her sister are sisters-in-law.
Since 'Schwägerin' (sister-in-law) describes a personal relationship, the word is almost always used with a possessive pronoun such as 'meine' (my), 'deine' (your), or 'seine' (his).
Meine Schwägerin ist eine sehr gute Freundin von mir geworden.
My sister-in-law has become a very good friend of mine.
sister
'die Schwester' and 'die Schwägerin' both belong to the area of family and refer to a female person. The important difference is the type of relationship: 'die Schwester' has the same parents as you. 'die Schwägerin' is connected to the family through marriage, for example the sister of one's spouse or the wife of one's own brother. Learners may confuse the words because both are close to the family. A practical rule is: for shared parentage, say 'Schwester'; for a connection through marriage, say 'Schwägerin'.

Meine Schwägerin kommt am Samstag mit meinem Bruder zum Essen.
My sister-in-law is coming for dinner on Saturday with my brother.
Meine Schwester und ich haben als Kinder oft zusammen im Garten gespielt.
My sister and I often played together in the garden as children.