Okay, so some people believe that a man named Barack Obama was not born in the United States, even though he said he was. And when he became the President of the United States, some people didn't like that and wanted to find a way to make him stop being the President.
So they looked for something that could prove he wasn't really born in the United States, because the Constitution says the President has to be born in the United States. They called themselves "birthers" because they were looking for proof of where Obama was actually born.
But most people think that Obama was telling the truth when he said he was born in Hawaii, and there is no real evidence that he wasn't. In fact, lots of people have looked into this and found that he really was born in Hawaii.
So even though some people still don't believe it, most people think that Obama was born in the United States and was allowed to be President.