Step 1: Understanding the Concept:
A wagering agreement, as defined in cases like \textit{Carlill v. Carbolic Smoke Ball Co.}, is an agreement where two parties, professing to hold opposite views touching the issue of a future uncertain event, mutually agree that, dependent on the determination of that event, one shall win from the other, and that other shall pay or hand over to him, a sum of money or other stake. Section 30 of the Indian Contract Act, 1872, declares wagering agreements to be void.
Step 2: Detailed Explanation:
The essential characteristics of a wager are:
1. Uncertain Event: The performance of the contract must depend upon the determination of an uncertain event.
2. Mutual Chances of Gain or Loss: Each party must have a chance to either win or lose.
3. No Other Interest: Neither party should have any interest in the event's occurrence or non-occurrence other than the sum or stake they will win or lose.
The core of a wager is uncertainty about an outcome. While in some rare cases a wager can be made on an unknown past event (e.g., betting on the result of a horse race that has already run but the result is not known to the parties), the quintessential and most common form of a wager relates to a future uncertain event. For example, betting on the outcome of a cricket match, an election, or the weather.
Given the options, "Future event" is the most characteristic and fitting answer. A wager cannot be on a present, known event. While a past, unknown event is a possibility, future events are the primary subject matter of wagers.