publicscope to make that property/method available from anywhere, other classes and instances of the object.
privatescope when you want your property/method to be visible in its own class only.
protectedscope when you want to make your property/method visible in all classes that extend current class including the parent class.
If you don’t use any visibility modifier, the property / method will be public.
More: (For comprehensive information)
- PHP Manual – Visibility