What is a statement that refers to something without mentioning it directly called?

Allusion is a figure of speech, in which an object or circumstance from unrelated context is referred to covertly or indirectly. It is left to the audience to make the direct connection.

In the arts, a literary allusion puts the alluded text in a new context under which it assumes new meanings and denotations.

William Irwin remarks that allusion moves in only one direction: "If A alludes to B, then B does not allude to A. The Bible does not allude to Shakespeare, though Shakespeare may allude to the Bible."