A more thorough explanation:

Definition: Communis error is a Latin term used in Scots law to refer to a common error or a long-standing practice that has no legal basis but is still upheld by the court.

Example: One example of communis error is the belief that a person can be arrested without a warrant if they are caught committing a crime. This practice has been followed for a long time, but it has no legal basis. However, the court may still uphold this practice as a communis error.

Explanation: The example illustrates how a long-standing practice that has no legal basis can still be upheld by the court as a communis error. Even though the practice is not legally valid, it has become so common that it is considered an error that the court would still recognize.