Definition
This phrase is used to express that helping a friend is a natural and expected part of friendship, often in response to a friend thanking you for a kind or special act.
"I really don't know how to thank you for helping me move." "Oh, it's nothing, what are friends for?"
"Thank you so much for preparing all of this for me; you’re so wonderful." "Don’t mention it, what are friends for?"
She always steps up when I need help. "I just did what I thought a friend should do," she said. "What are friends for?"