The Free On-line Dictionary of Computing (30 December 2018):

object method

    In object-oriented programming, a function
   that is called, or "invoked", on an object, as opposed to a
   class method which is invoked on a class.

   For example, a class "Person" might have an object method to
   return a person's name and a class method to return the number
   of people.

   An object method called on an object of class C may be defined
   by C or may be inherited (inheritance) from one of C's
   superclasses (class hierarchy).

   (2017-04-30)