Abstract: This paper discusses the essential aspects of term definition, and points out that the definition of a concept must fulfill the purpose to uniquely identify an object, i.e., it belongs to the class of the concept or it does not belong to the class of the concept. Also, the concept of the basic computer term “operating system” is analyzed in detail. Issues related to the definitions of “operating system” in most computer textbooks are discussed, and a new definition revealing the fundamental characteristics of this concept is given.

Key words: term, definition, operating system