What does estoppel refer to in legal practice?

Estoppel refers to a legal principle that prevents a person from asserting a claim or a fact that is contradictory to a previous position they have taken, especially if that position has been relied upon by others. When one party has made representations or conducted themselves in a way that another party has relied upon, the first party is 'estopped' from later denying the truth of those representations. This principle is fundamental in upholding fairness and consistency in legal proceedings.

In the context of the other choices, the concept of estoppel does not pertain to appealing decisions, which relates to processes for challenging rulings made by lower courts. Additionally, while estoppel can be involved in discussions regarding defenses against negligence claims, it is not specifically about those defenses themselves. Negotiation to settle claims involves discussions and agreements, but it does not encapsulate the nature of estoppel, which focuses on preventing contradictory assertions after reliance has been established. Thus, the correct understanding of estoppel as a legal impediment to denying a fact highlights its importance in ensuring fairness and protecting the reliance interests of parties in a legal setting.