From Yiddish, a local (New York City) loan word, in certain circles:

More or less literally: "Granny Fact"

"Old Wives Tale"

In the Hebrew, or, perhaps, Aramaic, of the Talmud, a "Maisa" is a deed. One asks for "Halacha L'maisa," or "The Law in application" that is, what you actually do.

It can also be used to mean fact. Someone tells you something astonishing and you say "L'maisa?" or "Really?"