In general usage, complexity tends to be used to characterize something with many parts in intricate arrangement. The study of these complex linkages is the main goal of complex systems theory. In science

Science

Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

 there are at this time a number of approaches to characterizing complexity, many of which are reflected in this article. In a business context, complexity management

Complexity management

Complexity management is a business methodology that deals with the analysis and optimization of complexity in enterprises. Effects of complexity pertain to all business processes along the value chain and hence complexity management requires a holistic approach...

 is the methodology to minimize value-destroying complexity and efficiently control value-adding complexity in a cross-functional approach.

Definitions are often tied to the concept of a "system

System

System is a set of interacting or interdependent components forming an integrated whole....

"—a set of parts or elements that have relationships among them differentiated from relationships with other elements outside the relational regime.