What is the purpose of a loop in programming?

The purpose of a loop in programming is to enable the execution of a block of code multiple times, typically based on a specific condition or a predetermined number of iterations. This construct is essential for tasks that require repetitive actions without having to write the same code multiple times, which enhances efficiency and readability in programming.

When a loop is used, it will continue to execute the block of code inside it as long as the specified condition evaluates to true. For instance, in a for loop, you can iterate a specific number of times, while in a while loop, the execution continues until the condition becomes false. This feature is crucial for automating repetitive tasks, such as processing items in a list, performing calculations iteratively, or repeatedly taking user input until a certain condition is met.

In contrast, the other options describe actions that do not accurately reflect the functionality of a loop. For instance, executing a block of code once relates to conditional statements, terminating a program's execution is typically an action associated with user commands or error handling, and declaring variables is a separate concept entirely that involves defining a space in memory to store data.