A more thorough explanation:

Definition: Conscientia rei alienae is a Latin term used in Scots law to refer to the knowledge that property held by one person actually belongs to another.

Example: If John knowingly buys a car that he knows belongs to Jane, he has conscientia rei alienae.

This means that John is aware that the car he is buying is not actually his, but belongs to Jane. He is therefore committing a legal offense by purchasing the car without Jane's permission.