If someone is “behind bars” it means that they are in jail (prison). If you watch a lot of American TV or movies you will hear this expression a lot. It’s one of those phrases you probably didn’t learn in class, but if you can use it, you’ll be one step closer to speaking English like a native speaker.
Here are a couple examples:
His dad is still behind bars. They haven’t seen each other in over 3 years.
This country is pretty strict. If you get caught selling drugs here they’ll put you behind bars for a few years.
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