What does the term "service brake" refer to in train operations?

The term "service brake" refers to the braking system utilized during normal train operations to control the train's speed and ensure safe stopping as needed. This type of brake is typically engaged during regular movement, allowing the train to slow down or come to a complete stop in response to signals, obstacles, or changes in the track.

In contrast, options referring to emergency brakes or parking brakes serve different purposes. Emergency brakes are designed for situations requiring immediate deceleration due to unforeseen circumstances, while parking brakes are employed to hold the train stationary when it's not in motion. Auxiliary brakes, mentioned in another option, are often used in specific situations, such as controlling speed when climbing or descending inclines, but do not encompass the broader function of regular train operation that service brakes provide.