The short answer
Jury nullification is a not-guilty verdict returned by a jury that believes the evidence fits the charge. The jurors have heard the case. They may agree that the accused did what the charge says. They return not guilty anyway, and the verdict stands.
That is the whole idea, and it is the same in every courtroom in the country. What differs, and differs a great deal, is how each jurisdiction's law deals with it.
Why the verdict is final
A not-guilty verdict is the one decision in a criminal case that nobody gets to revisit. Three rules about a criminal verdict make it so, and every state writes them in its own words: one about what a jury has to explain, one about what a judge can do with a verdict, and one about whether a person can be tried twice. Your state's chapter quotes its own version of each, with the citation.
What the judge tells the jury
Before a jury goes out to decide, the judge reads it the law. Most jurisdictions have a standard instruction on who decides the law and who decides the facts. Of the 52 jurisdictions this guide covers, 49 have one.
What those words are, and how firmly they are put, is a different thing in each place. Some instructions are a sentence. Some run to a page. A few say something no other state says. The exact wording a judge reads in your state is in its chapter.
What the written law says
Under the instruction sit the state's constitution, its statutes and its court rules. They do not all say the same thing about the jury's role in deciding the law. Of the 52 constitutions and charters, 23 address that role and 29 do not. 51 of the 52 jurisdictions require every juror to agree in a criminal case.
Those figures come from the chapters themselves, counted by the build each time the guide is made. Which group your state is in, and what its own text says, is what the chapter is for.
Three questions the chapters answer
Will a judge ever tell the jury about this? Can a defense lawyer argue it in court? Can a person called for jury service be excused for their views about the law? Each jurisdiction answers those three questions in its own rules and its own cases, and the answers are not the same from one state line to the next. Each chapter gives its jurisdiction's answers, and the source for each one.
Where this guide fits
JuryNull is a reference, not legal advice. It does not tell anyone what to do in a courtroom. What it does is collect the words that govern this question for every state, the District of Columbia and the federal courts: the constitution, the statutes, the court rules and the jury instructions. They are quoted where they can be quoted and explained in plain English where they cannot. Every one links to the official text behind it.
The general picture on this page is the same everywhere. The details are what a person called for jury service, or sitting in a courtroom, actually meets, and the details are in the chapters.