"Raining Cats and Dogs"

"Raining Cats and Dogs" did not make sense to me when I first heard it when I was in English as Second Language Class in elementary school. The image of cats and dogs falling from the sky like rain drops seemed only image that I could see from the phrase.

What I didn't know back in the day that there are many idioms in English. Idioms are phrases that does not make sense literally but it is commonly used that everyone know the meaning of it. If I literally translated it, it probably would not make any sense in other culture.

What is the meaning of  "Raining Cats and Dogs"?
"Raining Cats and Dogs" means it is raining very hard.

Have I heard anyone use it ?
Actually, I have heard people use it and not onlythat I had opportunity to use it on the rainy days. You may not need to know Rainig Cats and Dogs when you are still trying to learn simple phrases in English but now you know what it mean, you won't wonder what it means.