The access modifier is used define the accessibility of a member or type. The c# access modifiers are five types. They are,
  1. Public
  2. Protected
  3. Private
  4. Internal
  5. protected internal
Public - There is no restriction on accessing public modifier. The public method or type can be access from different assembly.

Protected - The protected method or type can be accessed from same class and derived class of that class.

Private - The private can be accessed only from that class.

Internal - The internal can be accessed from same name assembly but not by some other assembly like public.

Protected internal - The protected internal can be accessed by same assembly and derived assembly.