From MarineSpecies Traits Wiki
Definition of Systems approach:
The Systems Theory (Bertalanffy, 1968), states that complex, non-linear systems function
differently in vivo than a separate scrutiny of their component parts might indicate. The goal of the Systems Approach is to devise strategies to extract information on the functioning of complex systems that could not have been garnered from a sequence of subsystem-scale studies. Fundamentally, this requires the best-possible understanding of the processes and dynamics of asystem.
This is the common definition for Systems approach, other definitions can be discussed in the article