It means"let out the secret accidentally". In ancient Greek, people vote by counting beans of different colors people put into the container. But if the container is broken, the beans will be spilled over the ground and then the result is known in advance. "We were trying to keep it a secret from Sam, but Lisa spilled the beans."

To tell someone of a secret. Example: Rick spilled the beans to Dave about his secret birthday party. Hope that helps.

To spill the beans is an idiomatic phrase which means to reveal a secret. For example: when the child was being questioned about the missing candy, he spilled the beans and revealed that his sister had eaten it. In Spanish, the dictionary says that to spill the beans (sentido figurado) = descubrir el pastel (español de España), = destapar la olla (Am) In Portuguese, it may be: derramar o feijão