TITLE: Does "iff" mean "if and only if" $(\Longleftrightarrow)$?
QUESTION [6 upvotes]: Sometimes I do read in a sentence:
some statement iff another statement
At first I thought it is a mispelling, but then I realized, that I do encounter this at many different posts. Does this mean equivalence?

REPLY [4 votes]: Using your example:
some statement iff another statement.
This is a short-hand way of combining the "if-then" form of a statement, and its converse or the vice versa statement when they are both true:

if another statement, then some statement;

or
some statement, if another statement (1)


if some statement, then another statement;

or
another statement, if some statement  (2)

Combining (1) and (2) gives:
some statement iff another statement.