A claim is a set of operative facts creating a right enforceable in court. The term claim is generally synonymous with the phrase cause of action, though some contexts prefer to use one of the terms over the other. For example, in the field of insurance, you generally file a claim for coverage under a policy rather than file a cause of action for coverage under a policy.
Attempting to file a lawsuit in which no claim is present will result in the dismissal of that lawsuit under Federal Rule of Civil Procedure 12(b)(6) for failure to state a claim. As established in Ashcroft v. IQBAL and Bell Atlantic v. Twombly, a claim must be plausible on its face and establish more than the mere possibility that the defendant is liable to survive a 12(b)(6) motion to dismiss.
Legal claims are subject to the principles of res judicata and a party may therefore be unable to bring an otherwise valid claim to court due to claim preclusion. A party is precluded from raising any claim in a new lawsuit that was already adjudicated on the merits in a previous trial, as well as any compulsory counterclaim that they could have raised but did not raise in that previous trial.
In patent law, a claim is a technical description for each segment of the invention that the patent protects. Most patents include multiple claims. The first claim usually describes the whole invention in the broadest terms allowed by the USPTO. Subsequent claims describe - in increasingly precise terms - how each unit of the invention gets created.
[Last updated in July of 2022 by the Wex Definitions Team]