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Res Judicata
Res judicata means that once a court has made a final decision on a claim, the same parties cannot bring that same claim again in another lawsuit.
What it actually is
Res judicata is a legal doctrine that prevents re-litigation of a claim or issue that has already been finally decided by a competent court. It appears procedurally when a defendant argues that a lawsuit should be dismissed because the matter was already conclusively resolved in a prior case. The doctrine rests on the principle of finality, ensuring that litigation has an endpoint.
Why it matters in your case
If you are a party in a case, res judicata can stop you from suing (or being sued again) over the same dispute, saving time and expense. Practically, it means you must include all related claims you have in your first lawsuit, because later suits on the same core issue may be barred.
The common misunderstanding
Many people confuse res judicata with the broader concept of double jeopardy, but double jeopardy applies only in criminal cases. Res judicata applies in civil cases and bars a second civil lawsuit, not a criminal prosecution.
Get the actual rule
Definitions are orientation; rules are authority
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
Terms that travel with this one
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.