Due process is a right granted to every United States citizen by both the Fifth and Fourteenth Amendments to the Constitution. In general; the due process clauses of the law prevent the Federal government from depriving any citizens of their rights to property, life, and liberty as guaranteed by the Constitution.
The Fifth Amendment specifically states that no American citizen can "be deprived of life, liberty, or property, without due process of law." This Amendment was ratified in 1791 and applies only to the Federal government. In 1868, the Fourteenth Amendment extended citizens' due process rights to include every State, as well.
In its broadest sense, due process ensures that citizens cannot be deprived of their life, liberty, and property without reasonable warning and without the opportunity to defend themselves. Due process is a fundamental, constitutional guarantee that all legal proceedings will be fair and no laws regarding life, liberty, and property will be arbitrary, unreasonable, or capricious.
In practice, due process is the term used to mean that any legal proceedings dealing with life, liberty, and property will be conducted openly, fairly, and appropriately.