For example, in Hitchcock's North By North West, we, the audience, see the CIA reveal that the mystery man, Kaplan, doesn’t exist. However, the main character, Thornhill, played by Cary Grant, doesn’t know this and spends the entire second act looking for Kaplan (irony.) What he doesn't know might get him killed, and we are on the edge of our seats hoping he figures it out before it is too late. (tension.)
Recognition occurs when key information that the audience knows is finally revealed to a character. This often resolves tension and dramatic irony.
For example, in Hitchcock's North By North West, the tension of the second act is resolved when Thornhill is told Kaplan does not exist. However, a new tension is established with a Reveal, both he and the audience discover that Eve is working for the CIA and that Thornhill has unwittingly put her in grave danger.