What does the idiom "When it Rains it Pours" mean?

Hi there

Thank you for your question.

The phrase “When it rains, it pours” means that when something bad happens, other bad things or instances tend to occur at the same time as well, often all at once or in very quick succession of one another. It implies that problems come in waves all at the same time, instead of one bad thing happening now and then again at a much later stage. 

I hope this explanation answers your question and I look forward to answering any further questions you may have.