It's called the Uniform Access Principle, as I've already mentioned in a separate comment. Getting back to your example, it is not very useful without mentioning a language under examination. There is no single definition of OOP, and every language implements in a slightly different way.
There are languages where UAP is enforced by the syntax (eg. Eiffel, Smalltalk, Ruby) and languages where it's a matter of convention. But even in the latter it's considered a good practice to keep properties private and encapsulate them with accessors. Some even have dedicated features that help with that (auto-properties in C#, properties in Python).
There are languages where UAP is enforced by the syntax (eg. Eiffel, Smalltalk, Ruby) and languages where it's a matter of convention. But even in the latter it's considered a good practice to keep properties private and encapsulate them with accessors. Some even have dedicated features that help with that (auto-properties in C#, properties in Python).