Which of the following best defines 'estoppel'?

Estoppel is a legal principle that prevents a person from arguing something contrary to a claim they previously made, or from denying the validity of a statement they previously accepted. It generally operates under the idea that one cannot go back on their word if someone else has relied on that promise or representation to their detriment.

The correct definition involves the concept of involuntary relinquishment of a right, as it occurs not by choice or voluntary action, but due to the principle that a party cannot assert a right or claim that contradicts what they previously established. This principle helps to ensure fairness and reliability in legal proceedings and agreements.

In contrast, voluntary relinquishment refers to a choice made by an individual to give up a right, which does not encapsulate the essence of estoppel. A legal obligation to do something does not capture the concept of estoppel directly, as it suggests a duty rather than a limitation based on prior actions. Similarly, the risk of loss pertains to liability and insurance coverage rather than the legal implications of renouncing a right based on previous assertions or actions.