This article aims to understand the most fundamental operating principles of the phenomenal world and figure out how phenomena within the phenomenal world are interconnected. Causality is the most basic connection, rule, logic and fact of the phenomenal world, since everything in the phenomenal world is originally in the interconnection of three elements: cause, condition and effect. Finding the causal connection between things and utilising it to achieve the goal of avoiding harm and ultimately attaining happiness is the fundamental motivation for all human intellectual activities, including scientific research, philosophical discernment, and religious beliefs. The article gives a universal definition of causation as the primordial, underlying, transcendental, inherent, intrinsic, ultimate, essential, fundamental, inevitable, invariable, timeless, universal, complex, multidimensional, dynamic connection, law, logic, and fact among the three elements of cause, condition and result in the phenomenal world. The article explains in detail why the foregoing definition is universal from both ontological and epistemological perspectives.