a question regarding terminology

Hey, if there is a better place on the boards for this thread, please let me know, but I wasnt sure.

Okay, in KH-2 The Nobodies use paths of darkness to get around right? When they arrive anywhere, a vortex type portal appears, with what Im assuming is darkness flowing out.

Question: Does anyone know what the graphical term if for the darkness thats flowing out? Like, is it smoke?, is it fluid? is it ink-smoke? I know this may seem stupid, and the answer could probably be simply stated as 'Darkness', but I need a descriptive term that defines that effect or that substance. Usually everything has some sort of term. Like how when Xion disperses into sprites or whatever at the end, those are called pyreflies.
Im trying to create a similar effect of the "darkness" or the inky-smoke stuff, but I dont even know what to ask people. The closest ive come to finding a similar substance or effect in cinema, is with harry potter, the Ink-smoke effect they use for the death-eaters, and when they enter one of dumbledores keepsake memories.
Anyways, I really really would appreciate any type of assistance. Thank you.

 

hmm,

maybe