Laches is a legal term derived from the Old French lashes, meaning “remissness” or “dilatoriness,” and is viewed as the opposite of “vigilance”. The term refers to a lack of diligence and activity in making a legal claim, or moving forward with legal enforcement of a right, particularly regarding equity; hence, it is an unreasonable delay that can be viewed as prejudicing the opposing party. When asserted in litigation, it is an equity defence, that is, a defence to a claim for an equitable remedy. The person invoking laches is asserting that an opposing party has “slept on its rights,” and that, as a result of this delay, circumstances have changed, witnesses or evidence may have been lost or no longer available, etc., such that it is no longer a just resolution to grant the plaintiff’s claim. Laches is associated with the maxim of equity, “Equity aids the vigilant, not the sleeping once” who sleep on their rights. Put another way, failure to assert one’s rights promptly can result in a claim being barred by laches.
A defence lawyer raising the defence of laches against a motion for injunctive relief might argue that the plaintiff comes “ waltzing in at the eleventh hour” when it is now too late to grant the relief sought, at least not without causing great harm that the plaintiff could have avoided. In certain types of cases, a delay of even a few days is likely to be met with a defence of laches, even where the applicable statute of limitations might allow the type of action to be commenced within a much longer period. In court in the US, laches has often been applied even where a statute of limitations exists, although there is a division of authority on this point.
If a court does accept the laches defence, it can decide either to deny the request for equitable relief or to narrow the equitable that it would otherwise give. Even if the court denies equitable relief to a plaintiff because of laches, the plaintiff may still have a claim for legal relief if the statute of limitations has not run out.
Under the US Federal rules of civil procedure, laches is an affirmative defence, which means that the burden of asserting laches is on the party responding to the claim to which it applies.
The laches defence does not apply if the claimant was a minor during the time that the claim was not brought, so a party can bring a claim against a historical injustice when they reach their majority.
Res Judicata could be a phrase that has evolved from a Latin maxim, that represents 'the issue has been judged', that means thereby that the problem before the court has already been set by another court, between equivalent parties.