Friend of a friend (FOAF) is a phrase used to refer to someone that one does not know well, literally, a friend of a friend.
In some social sciences, the phrase is used as a half-joking shorthand for the fact that much of the information on which people act comes from distant sources (as in "It happened to a friend of a friend of mine") and cannot be confirmed. It is probably best known from urban legend studies, where it was popularized by Jan Harold Brunvand.
The acronym FOAF was coined by Rodney Dale and used in his 1978 book The Tumour in the Whale: A Collection of Modern Myths.
"L'homme qui a vu l'homme qui a vu l'ours" (French proverb) — similar French language proverb literally meaning The man who saw the man who saw the bear, in which the bear is never seen, only heard of.
"Un amigo me dijo que un amigo le dijo…" (Spanish proverb) — meaning literally A friend told me that a friend told him that…