An illegal immigrant is an immigrant who lives in a country without permission or in a way that is not allowed, or illegal. Millions of people around the world live in another country against the laws of that country.
Many of these people migrate to a country in secret. Many others come to the country legally as a visitor, then stay in the country when they should legally going home. Someimes, they work illegally and live in bad conditions. They usually move for similar reasons as other immigrants, but they don't legally have the right to be there.
In the US[change | change source]
Several immigrants illegally cross the Mexican border and enter to United States every year. In general, they are opposed by the Republican Party, which generally wishes to deport them, while in general Democrats want to help give illegal immigrants legal status. In 2016, Republican Donald Trump ran on a bid to build a wall on the Mexican-American border to prevent further illegal immigration.