Step 1: Understanding the Question:
This item assesses familiarity with standard English idioms, specifically requesting the definition of "to spill the beans".
Step 2: Detailed Explanation:
The phrase "to spill the beans" is an idiom that signifies accidentally or intentionally revealing a secret or hidden information.
Among the given choices, "To reveal a secret" accurately reflects the true meaning of this expression.
Step 3: Final Answer:
The correct choice is (B).