• A complex is a whole that comprehends a number of parts, especially one with interconnected or mutually related parts.

• In psychology, a complex is a group of mental factors that are unconsciously associated by the individual with a particular subject and influence the individual's attitude and behavior.

• In chemistry, a complex, or coordination compound or metal complex , is a structure consisting of a central atom or molecule weakly connected to surrounding atoms or molecules.

Mathematics

• A complex number is a number in the field of numbers which includes the real numbers and the imaginary numbers, of the form a + ib, where a and b are real numbers and i is the imaginary number equal to the square root of -1.

• A complex is an element of a complex algebra or field of sets.

• A simplicial complex is a space that can be divided into fully adjacent triangles.

• A complex system is a system comprised of interconnected simple parts that exhibits a high degree of computational complexity from which emerges a higher order behavior. Complex systems beave in a non-deterministic fashion and cannot be broken down to groups of series and parallel components.