A more thorough explanation:

Custodial interrogation

Custodial interrogation is when the police question someone who is being held in connection with a criminal investigation. The person being questioned is considered "detained" if they are not free to leave. This can happen even if they are not under arrest. For example, if the police pull someone over for a traffic violation and keep them from leaving until they provide their license and registration, that person is considered detained.

Thanks to a famous court case called Miranda v. Arizona, the police must inform the detained person of their Miranda rights before questioning them. If they don't, any statements the person makes cannot be used in court.

Imagine that the police suspect someone of stealing a car. They bring that person to the police station for questioning. During the interrogation, the police ask the person if they stole the car. This is an example of custodial interrogation because the person is being held and questioned in connection with a criminal investigation.

Another example is if the police stop someone on the street and start asking them questions about a crime. If the person is not free to leave, they are considered detained, and any questioning would be considered custodial interrogation.

These examples illustrate how custodial interrogation involves questioning someone who is not free to leave. It's important for the police to inform the person of their Miranda rights before questioning them to ensure that any statements made are admissible in court.