Wide interface and narrow Interface

Wide interface:
Iinterface1 = interface
// Method list
End;

Narrow interfaces: object interfaces. Interface declarations are similar to classes, but they cannot be directly instantiated or implemented by themselves. Instead, they are implemented by classes that support interfaces.
Type
Tstrategy = Class (tobject) // abstract policy
Public
Procedure hello; virtual; abstract;
End;

Tcontext = Class (tobject) // Context
Private
Fstrategy: tstrategy; // reference an existing object (narrow Interface)
Procedure setstrategy (value: tstrategy );
Public
Procedure contextinterface; // assign responsibility to an existing object
Property Strategy: tstrategy read fstrategy write setstrategy;
End;