Lawyers and newspapers are always going on about due process of law. That this or that action violates due process.
SO WHAT IS DUE PROCESS?
First and foremost, due process requires that anybody who asks a court to rule in his favor must describe what he wants, why he wants it, and NOTIFY the other side that there is a matter in front of the court. The person sued gets a chance to answer and to have a court hearing, often with a jury trial, to decide the matter.
In civil matters, the two sides have to exchange information relevant to the case. In criminal matters, the government has to provide all information that they have regarding the case to the arrested person.
A person cannot be arrested by law enforcement unless the law officer states why the person is arrested, and lists the charges. The arrested person does not have to tell the police anything. The arrested person gets a fair trial, by jury, and an attorney to defend him. Sometimes a court will let a person out of jail on a habeas corpus petition because of a violation of due process.
A violation of due process is also a fancy way to say, "This is unfair. It is so unfair that justice will not be done."
The above description cannot possibly cover all of the aspect of due process. Volumes of court decisions and legal treatises have been written about due process.
DUE PROCESS of law is guaranteed by the 14th Amendment to the US Constitution. The term, in Latin, of course, goes back to the 1200's as part of the English Magna Carta.