Laches is the legal doctrine that an unreasonable delay in seeking a remedy for a legal right or claim will prevent it from being enforced or allowed if the delay has prejudiced the opposing party. The doctrine is an equitable defense that seeks to prevent "legal ambush" from a party who is negligent in failing to timely make a claim. It recognizes that the opposing party's ability to obtain witnesses and other evidence diminishes over time, due to unavailability, fading memory, or loss. Disallowing the negligent party's action on the ground of laches is a form of estoppel.
Laches is an equitable form of estoppel based on delay. The theory behind allowing the defense is that the law shouldn't aid those who "sleep on their rights". For a defense of laches to succeed, it must be proven that the party invoking the doctrine has changed its position as a result of the delay, resulting in being in a worse position now than at the time the claim should have been brought. For example, the delay in bringing the claim may have caused much larger potential damages to be awarded; the ability to pay the claim is lacking due to assets being otherwise used in the meantime; the property sought to be recovered has already been sold; or evidence or testimony may no longer be available to defend against the claim.