Any connection device that provides a number of degrees of freedom in a relation between two elements or structures.
This notion was introduced by the French physiologist P. VENDRYES (1973, p.88) and is a generalization from the articulations between bones.
VENDRYES explains that no movement would be possible if bones were rigidly united. Freedom of movement depends on the possibility to adopt a number of different relative positions, as flexion, extension, rotation, etc… However movement could not be coordinated if the relations were totally undefined. The ligaments and their connections with the bones and muscles provide a more or less extensive program for mobility relations. This program is framed within defined determinisms, but, at the same time, within this frame it allows for a variety of combinations, and much more so when there is a chain of articular relations, as for example from the shoulder to the fingers. In VENDRYES terms: "Thanks to its elasticity, a muscle admits articular indeterminism; by its contractibility it imposes a determinism" (p.90) As a result, a number of more or less random options do exist. But any defined movement selects only one and thus imposes at some moment, in some situation and for a limited time, a specific determinism.
According to VENDRYES the articular relation concept can be generalized to any relation wherein a number of undefined possibilities coexist, but where only one can be selected (excluding all others) at any specific moment.
As an example, he gives the articular relation between words in a language.
The analogy with decision mechanisms in general is also striking.