What is the word for when you say one thing but mean another?

What is the word for when you say one thing but mean another?

People who say things facetiously are being a little bit sarcastic, saying one thing and meaning another, or treating a serious subject in a funny way.

What is a word that means something is both good and bad?

agathokakological. (nonce word) composed of both good and evil.

What is the word for something that represents something else?

something used for or regarded as representing something else; a material object representing something, often something immaterial; emblem, token, or sign. a letter, figure, or other character or mark or a combination of letters or the like used to designate something: the algebraic symbol x; the chemical symbol Au.