De novo means a court hears a case from the beginning, as if the previous decision never happened, giving you a fresh chance to present your arguments.
In a legal appeal, a de novo review means the appellate court does not defer to the lower court's findings but re-examines the legal issues independently. It most commonly appears when a trial court's legal conclusions are challenged, rather than its factual findings, and can also occur when a case is retried in a new court after an initial decision is set aside.
If your case receives de novo review, the appellate court will look at the law from scratch, which can be favorable if the lower court made a legal error but unfavorable if you relied on the lower court's factual findings. It means you are not stuck with a prior bad legal ruling, but you also cannot assume the new court will agree with the old one.
Many people confuse de novo review with a full retrial of facts, but it usually applies only to legal questions, not factual disputes. A de novo hearing in a trial court (like after a small claims appeal) does involve a new trial, but on appeal it typically means only legal issues are reconsidered.
Get the actual rule
This page explains the concept. When it matters to your case, read the rule that governs it in your court — we hold Texas, federal and Washington court rules word for word, and every state's official resources are on the state pages. If someone cites a case at you, check that it exists first.
Related
General explanation, not legal advice, and not specific to any state — procedures and deadlines vary by jurisdiction and court. If you can get a lawyer or free legal aid, do: every real option.