To determine the correct answer, let's go through each option and explain why it is right or wrong:

A. The result of a user's action: This option is correct. An event is typically defined as the result of a user's action. In computer programming, an event can be triggered by user input, such as clicking a button or typing on a keyboard. The system responds to these actions by executing certain code or performing specific actions.

B. The result of a party: This option is incorrect. An event is not related to a party. In the context of computer programming, an event refers to user actions and their corresponding effects.

C. Code to force a user's action: This option is incorrect. An event is not code designed to force a user's action. Instead, events are typically triggered by user actions and are followed by specific reactions or responses from the system.

Therefore, the correct answer is A. The result of a user's action.