What is a Conversion?

simply explained, a Conversion is a Long stock AND a synthetic Short position; for example :

say AAPL is at $200 now.

Long AAPL @ $200 (this is the Long stock position)
Short AAPL 200 Call + Long AAPL 200 Put (this combo is the Short synthetic stock)

If stock price moves up, the Long stock position profits but the Short synthetic stock position loses about the same amount, resulting in very little fluctuation in the P/L.

Conversions are as good as flat positions (not totally, but very close). Hence, there is no directional risk in Conversions.

since Conversions can hardly make money (not that it can't, just rather difficult), the question that is begging to be asked is "why would anyone establish a Conversion?"

answer: no retail player in the right mind, except to temporarily mitigate all directional bias risks, should establish such Conversions.

but this doesn't yet directly explain why Conversions and Reversions cause stock markets activities to spike on expiration days...