This video was posted by the NYTimes and goes over checking and comparing the different statements that Trump has said about immigration. Often times his staff supports him and his statements, and instead of them apologizing for them, they call them “alternative facts”. They are not “alternative facts” though they are actually falsities which are statements that are untrue, incorrect, and insincere.
“Alternative facts” is originally a law term which describes the inconsistencies of facts put forth in a court, when there is plausible evidence to support both sides of the fact. In this video below you can see the different sides of “facts” that Mr. Trump speaks about.