Step 1: Understanding the Concept:
The question asks for the basic definition and effect of the doctrine of Estoppel in the law of evidence.
Step 2: Key Formula or Approach:
The principle of estoppel is codified in Section 115 of the Indian Evidence Act, 1872.
Section 115. Estoppel.— "When one person has, by his declaration, act or omission, intentionally caused or permitted another person to believe a thing to be true and to act upon such belief, neither he nor his representative shall be allowed, in any suit or proceeding between himself and such person or his representative, to deny the truth of that thing."
Step 3: Detailed Explanation:
The essence of estoppel is that a person is precluded or "estopped" (stopped) from going back on a previous representation (of fact) they made, if another person has relied on that representation to their detriment. It is a rule of equity and fairness designed to prevent a person from taking unfair advantage by contradicting a previous statement or action. Thus, it effectively stops a party from asserting something contrary to what they previously represented, or denying a fact they previously affirmed.
The other options are incorrect. Estoppel does not prevent a party from appearing in person or from hiding evidence (which is dealt with by other procedural rules).
Step 4: Final Answer:
Estoppel is a rule by which a party is Stopped from asserting or denying a fact.