Legal Latin that literally means an inconvenient forum or disagreeable forum. It refers to a situation where a particular court or tribunal does properly have jurisdiction over a case or dispute and venue likewise is proper, but the location is a very difficult place for one of the parties, typically the defendant. This may be because of evidence being located elsewhere, witnesses, or just the cost and inconvenience of litigating in a distant forum. The result is usually a motion to transfer the case to a more convenient court or tribunal. If such a transfer takes place the usual effect is that the substantial law of the case remains unchanged, but the procedural law and rules of the transferee court apply to the case – since procedural rules can have a large impact on a case – and in the US jury composition, this is not a trivial issue.
Forum non-conveniens and transfer motions are a frequent reaction to forum shopping, but may themselves also constitute an effort by the party advancing them to forum shop. It is usually wise to file a transfer motion as early in a case as possible as courts are usually reluctant to transfer cases after they have been in that court for key procedural events such as answers, motions to dismiss and scheduling orders. It is also wise when selecting a forum court or tribunal to take care not to allow a defendant an easy basis for arguing forum non-conveniens. Factors that might make a judge inclined to transfer are a very busy court docket, parallel proceedings in the court that would receive the case, the willingness of the other court to accept the transfer and, sometimes, a suspicion that the plaintiff’s original choice of court was driven by fairly blatant forum shopping.
So for example if a case is filed by a plaintiff in city-A, the court will not like to override the plaintiff’s choice, but if for example the plaintiff has few or no substantive contacts with forum A, while the it does have a presence in city-B, the evidence is mostly near city-B, the witnesses are there, and maybe there is even local law in city-B is applicable in the case, this would tend to favour transferring the case. On the other hand if the defendant is not seriously inconvenienced and the plaintiff would be, a transfer is unlikely.