In Integral Relational Logic, an association is an associative relationship that is non-hierarchical, where there is no obvious structural relationship between concepts. Such relationships are what makes the world we live in so complex. In my experience, hierarchical structures are much easier to understand.

Another term for non-hierarchical relationships is heterarchy, which Warren S. McCulloch introduced in 1945, from Greek Eteros ‘other, different’. At the time, he was studying the topology of nervous nets, where A is preferred to B, B to C, and C to A, with none being summum bonum, like in the rock-paper-scissors game.

In 1979, in Gödel, Escher, Bach, Douglas R. Hofstadter adopted this term to denote computer programs in which there is no single ‘highest level’ or ‘monitor’, although this use of the term does not seem to have caught on, as far as I aware. For instance, in object-oriented modelling systems, like the Unified Modeling Language, association is generally preferred.