An "alien" in England was someone who was born outside of the monarch's dominions and who did not have allegiance to the monarch. Aliens were not allowed to own land and were subject to different taxes from subjects.
Some people who live in Australia are not Australian citizens - they are either permanent residents; temporary residents; or illegal residents (technically called "unlawful-non citizens"). Most non-citizens (i.e. those who lack citizenship documents) travelling to Australia must obtain a visa prior to travel. The only exceptions to this rule are members of the British royal family, and holders of New Zealand passports and citizenships who may apply for visas after travel according to the Trans-Tasman Travel Arrangement.