The United States government is a Limited Government because there are laws that protect the rights of the people. We have a constitution that limits what the government can do to the people. Those laws protect and guarantee our personal freedoms.
An unlimited government is a government where there are no limits on what the government can do to its people. The people have very few, if any, rights and the government treats them like they want to. Examples are communist countries of Cuba and North Korea and also totalitarian government like Syria.