1.
slithering; wriggling; squirming along
A mimetic word (擬態語) for the smooth, twisting movement of a long thin creature such as a snake, eel, or worm — and by extension for anything long that moves the same way.
Almost always used of living things that have no legs. The image is unsettling more often than not, so にょろにょろ carries a faint shudder that neutral うねうね does not.