Meaning of “illegal” - Learner’s Dictionary

illegal

adjective us uk /ɪˈliːɡəl/
Extra Examples
the illegal practice of copying CDsthe illegal purchase of gunsBoth men admitted taking illegal drugs.It's illegal to buy alcohol until you're 21 in many states.Police raided the house and found illegal weapons.

B2 not allowed by law:

illegal drugs/weapons
[ + to do sth ] It is illegal to sell cigarettes to anyone under 16.
illegally adverb

B2

an illegally parked car

(Definition of “illegal” from the Cambridge Learner’s Dictionary © Cambridge University Press)