shadow person

A shadow person is a dark, humanoid figure glimpsed at the edge of vision, typically interpreted as a paranormal entity or hallucination.

Reports describe featureless silhouettes that seem to watch or move just before disappearing.

Shadow people appear in folklore, horror fiction, and accounts of sleep paralysis or stimulant psychosis: I kept seeing shadow people after three days without sleep.

The term straddles supernatural belief and clinical explanation.