Flowing ossifications are seen in diffuse idiopathic skeletal hyperostosis (DISH).
They are defined as heterotopic ossifications involving the anterior longitudinal ligament, paraspinal connective tissues and annulus fibrosus of at least four contiguous vertebral bodies and are originally described on lateral radiographs of the spine. Typically there are radiolucencies between the anterior aspect of the vertebral bodies and the flowing ossifications of the anterior longitudinal ligament. The radiolucencies again classically end at the level of the vertebral endplates.
Although often used synonymously, they actually have their own definition.
As always in those cases, one has to decide for oneself, if one wants to be a "lumper" or a "splitter".