This paper deals with terminology as a characteristic feature of the language used in science and technology. The lexical units in question serve the communication needs and demands of particular discourse communities, i.e., experts in different branches of science and specializations. Terminology precisely describes reality, carries specific information on the phenomena and relationships between them and helps to avoid shifts in meaning during the process of communication. In comparison with other spheres of life where shifts in meaning are common, in science and technology, changes in the information transferred are unacceptable and may lead to serious consequences. This paper focuses on various aspects and approaches to this part of the lexical system. Examples from the English language for Electrical Engineering and Communication Technologies provide an insight into different criteria for classifying units as terms, lexical patterns and semantic relationships between the individual constituents. Other features, qualities and functions of terminology, such as the stabilizing reality, interconnection between explicitness and implicitness or description of progress reflecting a unique attitude to reality are also discussed.