Iterators act on a very important role in the abstraction of loop control mechanism and research on reusable software．Its research history is over ten years．However until nOW there iS no precise and unified definition about it yet．which affects one to understand its meaning heavily and hinder its widespread application．Based on analyzing and studying the limitations of fl variety of concepts of iterators in this paper，the authors define iterator as a abstract data type inside a combined data type and obtain a universal iterator pattern，then present the concepts and patterns of separate iterators and integrated iterators．Finally they illustrate its roles and usage by examples．