it's an idiom, mom!

While driving Abbie to her friend's house yesterday, there was a light drizzle and we had the following conversation.

Abbie: It's raining cats and dogs out here!

Me: Cats and dogs, huh?

Abbie: (sigh) It's an idiom, mom! (complete with sass and eye roll)

Then I laughed as I realized how long it has been since I had elementary English, because truthfully I would have had to look up the definition to be sure I knew what an idiom was. It's a good thing my kids are in school to remind me off all the things I learned once upon a time!