Translation

違法の / 非合法の / 法律に反する

Meaning

Illegal means against the law. It is stronger than not allowed because it usually points to a law, regulation, or criminal rule, not just a school or house rule. Do not confuse it with illegitimate, which can also mean invalid or not recognized.

Examples

• その地域で廃棄物を捨てることは違法です。
  Dumping waste in that area is illegal.
• 会社は違法な価格操作で罰金を科されました。
  The company was fined for illegal price fixing.