Complexity (glossary)

(1) The degree to which a system's design or code is difficult to understand because of numerous components or relationships among components

(2) Pertaining to any of a set of structure-based metrics that measure the attribute in (1); (3) The degree to which a system or component has a design or implementation that is difficult to understand and verify. (ISO/IEC 2009)

Source

(1) and (2) ISO/IEC. 2009. "Systems and Software Engineering Vocabulary (SEVocab)" - ISO/IEC 24765. in International Organization for Standardization (ISO)/International Electronical Commission (IEC) [database online]. Geneva, Switzerland, 2009 [cited December 21 2009]. Available from http://pascal.computer.org/sev_display/index.action.