A police box is like a little shed or booth that the police can use to keep people safe and help them when they need it. It’s kind of like a tiny police station that is outside in the streets.
Police boxes were first used in the UK a long time ago, before people had cell phones, computers or walkie-talkies. They were a way for the police to communicate with each other and for people to talk to the police if they had a problem, like if they were lost or hurt.
Inside the police box, there is usually a telephone, a radio, and a little desk. The police officer who is inside the box can talk to other police officers and get help quickly if they need it. They can also talk to people who come to the box for help.
Some people might recognize the police box as the TARDIS from the TV show Doctor Who. Although the TARDIS isn't real and can travel through time and space, it was inspired by the real-life police boxes which were once commonly seen on the streets of the UK.