formal

The definition of formal is something that follows rules, is a dressy or important occasion, or something that has official sanctioning or approval.

(adjective)

An example of formal is a dinner party at a mansion where everyone dresses up in fancy clothes and is very polite.
An example of formal is when a judge gives official approval of something.

See formal in Webster's New World College Dictionary

adjective

of external form or structure, rather than nature or content
of the internal form; relating to the intrinsic or essential character or nature
of or according to prescribed or fixed customs, rules, ceremonies, etc.: a formal wedding
1. having the appearance of being suitable, correct, etc., but not really so
2. stiff in manner; not warm or relaxed
1. designed for use or wear at ceremonies, elaborate parties, etc.: formal dress
2. requiring clothes of this kind: a formal dance
done or made in orderly, regular fashion; methodical
very regular or orderly in arrangement, pattern, etc.; rigidly symmetrical: a formal garden
done or made according to the forms that make explicit, definite, valid, etc.: a formal contract
designating education in schools, colleges, etc.
designating or of the level of language usage characterized by expanded vocabulary, complete syntactic constructions, complex sentences, etc.

Origin: ME < L formalis < forma, form

noun

See formal in American Heritage Dictionary 4

adjective

a. Relating to or involving outward form or structure.
b. Being or relating to essential form or constitution: a formal principle.
a. Following or being in accord with accepted forms, conventions, or regulations: had little formal education; went to a formal party.
b. Executed, carried out, or done in proper or regular form: a formal reprimand; a formal document.
a. Characterized by strict or meticulous observation of forms; methodical: very formal in their business transactions.
b. Stiffly ceremonious: a formal manner; a formal greeting; a formal bow to the monarch.
Having the outward appearance but lacking in substance: a formal requirement that is usually ignored.