A more thorough explanation:

The doctrine of acquired rights is a legal principle that states that once a right has been obtained, it cannot be taken away by later laws or regulations. This means that if someone has a legal right, it cannot be reduced or eliminated by new laws or regulations.

For example, if a person has a copyright on a book, the doctrine of acquired rights would prevent the government from passing a law that would reduce the length of time that the copyright is valid. The copyright holder has already acquired the right to control the use of their work for a certain period of time, and this right cannot be taken away.

Another example of the doctrine of acquired rights is in property law. If someone has owned a piece of property for a long time, they may have acquired certain rights to use the property in a certain way. If the government passes a law that restricts the use of the property, the owner may be able to argue that they have acquired the right to use the property in a certain way and that the new law cannot take away that right.