What is the meaning of Illegal?

Not authorized by law.

Contrary to or forbidden by law, especially criminal law.

Breaching certain enacted statutes of positive law; not lawful, not legal (cf. immoral, unethical)

Forbidden by established rules.

Totally fictitious, and often issued on behalf of a non-existent territory or country.

Being or doing something illegally.

Being an illegal immigrant; residing in a country illegally.

Describing a programming operation that is not allowed by the operating system.

An illegal act or technique.

Contraband, esp. illegal substances such as drugs.

An illegal immigrant.

A spy operating abroad illegally and under non-official cover, without visible ties to his or her country’s authorities.

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Pre-reform spelling (used until 1943 in Brazil and 1911 in Portugal) of ilegal.

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Source: wiktionary.org