The visibility of a class, a method, a variable or a property tells us how this item can be accessed.

Public:
The member can be reached from anywhere.
This is the least restrictive visibility.
Enums and interfaces are, by default, publicly visible.

Protected:
Members can only be reached from within the same class, or from a class which inherits from this class.

Internal:
Members can be reached from within the same project only.

Protected Internal:
The same as internal, except that also classes which inherits from this class can reach it members, even from another project.

Private:
They can only be reached by members from the same class.
This is the most restrictive visibility.
Classes and structs are by default set to private visibility.

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