Answer 1: Feels like a homework question (which I, for one, hate being asked here), but, what the heck, I'll bite...
"Due process of law" is a phrase which refers to the process of someone being either:
a) wronged by another and having the right to sue (as plaintiff) the wrong-doer (the defendant) in a court of civil law; and be financially compensated by said defendant, if the Court (or a jury empaneled thereby) agrees with the plaintiff; or,
b) prosecuted (as defendant) and put on trial by the state (the plaintiff) in a court of criminal law if the defendant has been arrested and charged with a crime (and, if s/he can post it, released on bail pending trial); and then be either acquitted (found not guilty, and released), or convicted (found guilty and then punished by fine and/or jail/prison time, or both) by the Court (or a jury empaneled thereby).
Bringing a matter between two parties -- be it civil or criminal -- before a court of law, and having said Court decide who wins, and then everyone agreeing to abide by the Court's decision, is called "due process" or "due process of law."
The "due process of law" is important because without it,
a) people would be settling their civil differences by doing things like physically fighting or killing one another; and/or,
b) the citizenry would be punishing those whom it believes to be criminals by doing things like dragging them into the town square and hanging them from tree limbs!
And so, then, the "due process of law" keeps us all civilized, and not acting like a bunch of thugs or a big mob. Uncivilized thugs and/or mobs jump to conclusions, and usually don't bother to give the other party a chance to defend himself/herself. We need the "due process of law" to ensure that parties who are accused of things, either civilly or criminally, get a fair chance to try to prove that they didn't do it. Or, more accurately, at least in the case of criminal defendants, because our system of justice in the US assumes everyone is innocent until they're actually proven guilty, then the "due process of law" ensures that the accuser can actually prove -- beyond a reasonable doubt -- that the accused is actually guilty.
Without the "due process of law," we're all just like a bunch of cave men, running around killing other cave men for things as simple as stealing a little of their food, or warming himself at one's fire.
The "due process of law" ensures that punishment is exacted only against those are are proven, by the process, to be deserving; and it further ensures that whatever is the punishment is reasonable, and fits the circumstanes.
John Adams (one of our nation's founders, and also the 2nd President of the United States) once wrote, in his 7th "Novanglus" letter, published in the Boston Gazette in 1774, that we are "a government of laws and not men." Though it's actually a notion that has existed since ancient Greece, and so was likely paraphrased by Adams from something Voltaire or his likes had written, it's nevertheless a very famous and important thing attributed to Adams in this nation's history which has been subsequently quoted by politicians, lawyers, judges, journalists, authors, and seemingly countless others. It means that our laws, and the system of "due process" both specified and required by them, is more important than any person, our group of persons, and what they either want or do.
Due process of law is important because it protects the rights of citizens. The fifth and fourteenth amendments to the United States Constitution each contain a due process clause.
Because once it is denied to one, no one is protected by the law.
Procedural due process
He wanted a prosecution quickly, but he had to wait for due process of law first.
Procedural due process means that the rule of the law will be obeyed.
Due process. In other words a process must be followed.
Law
substantive due process
due process of law
"Due process of law".
The word due process is best defined in one word--fairness.
substantive due process
Substantive due process addresses a law's fairness, while procedural due process addresses how a law is implemented.