protected:
The type or member can be accessed only by code in the same class or struct, or in a class that is derived from that class.
internal:
The type or member can be accessed by any code in the same assembly, but not from another assembly.
protected internal:
The type or member can be accessed by any code in the assembly in which it is declared, or from within a derived class in another assembly. Access from another assembly must take place within a class declaration that derives from the class in which the protected internal element is declared, and it must take place through an instance of the derived class type.
private:
The type or member can be accessed only by code in the same class or struct.
public:
The type or member can be accessed by any other code in the same assembly or another assembly that references it.