Definition of "Formal" :

noun: a gown for evening wear

noun: a lavish dance requiring formal attire

adjective: refined or imposing in manner or appearance; befitting a royal court

adjective: being in accord with established forms and conventions and requirements (as e.g. of formal dress)

"Pay one's formal respects."

adjective: (of spoken and written language) adhering to traditional standards of correctness and without casual, contracted, and colloquial forms

"The paper was written in formal English."

adjective: logically deductive

"Formal proof."

adjective: characteristic of or befitting a person in authority

"Formal duties."

adjective: represented in simplified or symbolic form