Time for another Ginseng English idiom! Today's idiom is "a dime a dozen," which means very common. 

As you may know, a dozen means 12. We use this word frequently to talk about buying things:

a dozen eggs:

a dozen donuts: 拎拎拎拎拎拎拎拎拎拎

a dozen roses: 屢屢屢屢屢屢屢屢屢屢屢

And a dime is a coin worth $0.10 in America: 


So, if something costs a dime for a dozen, it's really cheap, so it must be really common. This is a metaphor, though, so it isn't literal. Here are some examples: 

Beach towels are a dime a dozen in Florida.

Many people think old baseball cards are valuable, but they're a dime a dozen.

Cell phones used to be for rich people only, but now they're a dime a dozen.

If you like these English idioms, check these out!