Open/closed design principle states “software entities (classes,

modules, functions, etc.) should be open for extension, but closed

for modification”.

Open/closed principle term was originated by Bertrand Meyer in

his book Object Oriented Software Construction.

As per this principle, if a module is available for extension then it

is considered open. If a module is available for use by other

modules then it is considered closed.

Further Robert C. Martin has mentioned it as O in SOLID principles

of Object Oriented design.

It is used in State and Strategy design patterns. Context class is

closed for modification. But new functionality can be added by

writing new strategy code

https://www.baeldung.com/java-open-closed-principle#:~:text=As%20the%20name%20suggests%2C%20this,be%20extended%2C%20but%20not%20modified.