Plain English Meaning
Very short moments where a tired person's brain switches off without them realising it. They look awake, but for a second or two they are not actually taking anything in.
Full Definition
Brief, involuntary lapses of consciousness lasting from a fraction of a second up to about 30 seconds, during which a fatigued person stops processing external information even though their eyes may remain open. The person is typically unaware the lapse occurred.
Context Anchor
Seen in human factors and fatigue discussions, especially when studying obstacles to staying aware in the cockpit.
Derivation
From 'micro' (Latin/Greek root meaning very small) and 'sleep'. The name captures the key idea: these are tiny episodes of sleep that intrude into waking activity.
Why Pilots Care
A pilot in a microsleep can miss radio calls, , or without any that awareness was lost.