• (n.) One of the articular processes of a vertebra, of which there are usually four, two anterior and two posterior. See under Vertebra.
(zi″gә-pof´ĭ-sis) the joint between two adjacent vertebrae; called also facet joint.
Zyg`a·poph'y·sis noun ; plural Zygapophyses . [ Greek 
zygapophysis An articular process of a vertebra.
Greek zygon = yoke, apo = from, physis = growth; the articular process of a vertebra. The downward "growth" of the vertebra above articulates with the upward "growth" of the vertebra below, forming a zygapophyseal joint.
one of the four processes of a vertebra, occurring in pairs that interlock each vertebra with the vertebrae above and below.