#450 – Interfaces Should Normally Start with the Letter ‘I’

Interface names will typically start with the letter I, to help distinguish them from classes.

    interface IMoo
        void Moo();

Starting the name of an interface with the letter I is only an agreed-upon convention.  The name of the interface could actually be any valid type name.  But starting the interface name with the letter I helps readers of your code realize that the type is an interface type, rather than a class.