Plain English Meaning
The early, just-starting part of a spin — after the wing has stalled and the airplane has begun to rotate, but before the spin has settled into a steady pattern.
Full Definition
The phase of a spin that begins when the airplane stalls and starts to rotate, and ends when the spin becomes fully developed. It typically lasts about 4 to 6 seconds, or roughly the first two turns, during which the rotation, pitch attitude, and airspeed have not yet stabilized.
Context Anchor
Seen in spin awareness and spin recovery training, especially when describing the first moments after a stall turns into a spin.
Derivation
From Latin 'incipere', meaning 'to begin'. An incipient spin is literally the 'beginning' spin — it has started but is not yet fully formed.