The short-run fluctuations in economic activity that can cause output to be above or below the long-run trend are called:

Business Cycle

Explanation:

Business Cycle -

It refers to the upward or downward movement of the gross domestic product, is known as business cycle.

It is also known as trade cycle.

These movement are short - run, i. e., for very short time span.

Hence, from the given information of the question, the correct term is business cycle.