Let’s go to class, shall we?
Illegal: adjective.
1. Contrary to or forbidden by official rules, regulations, etc.
Alien: noun.
1. A resident of one country who was born in or owes allegiance to another country and has not acquired citizenship by naturalization in the country of residence.
2. Adjective. A person who resides under a government or in a country other than that of one's birth without having or obtaining the status of citizenship there.
They are humans but they are illegal aliens.