As

As

The keyword as is used to cast (use one variable type as if it were another type)

procedure TmainForm.selectionGridDrawColumnCell(Sender: TObject; const Rect: TRect; DataCol: Integer; Column: TColumn; State: TGridDrawState);
begin
     (Sender As TDBGrid).DefaultDrawColumnCell(Rect,DataCol,Column,State);
end;

here the Sender variable of type TObject is being cast as type TDBGrid

As is an Object Pascal and a Borland Delphi extension.