(physiology) Chiefly preceded by the: something which is below the limen or threshold of conscious perception.

(by extension) An advertisement, a message, etc., which is conveyed in a manner that a person is unaware of being influenced by it.

(physiology) Of a stimulus: below the limen or threshold of conscious perception, especially if still able to produce a response; also (generally), below the threshold where a response can be produced.

(by extension) Of an advertisement, a message, etc.: conveyed in a manner that a person is unaware of being influenced by it.