1. Describing a group of people:
* Friends of friends - This is the most common and grammatically correct way to refer to a group of people who are friends with your friends.
2. Describing a specific person:
* Friend of a friend - This is the correct way to refer to one specific person who is a friend of your friend.
3. Using the term as an adjective:
* Friends-of-friends - This is correct when using the phrase as an adjective, as in "Friends-of-friends event".
Here's a breakdown of the different uses:
* "I went to a party with some friends of friends." (referring to a group)
* "I met a friend of a friend at the coffee shop." (referring to one specific person)
* "The event was open to friends-of-friends." (using the phrase as an adjective)