In economics, the term risk neutral is used to describe an individual who values
risk at a constant value. Risk neutral is in between risk aversion and risk seeking, and a risk neutral individual will accept exactly the same interest rate for all assets.
The value that a risk-neutral individual assigns to a financial instrument is usually different from the expected value of the financial instrument based on market prices. Because real market prices will be
affected by the price the market is willing to pay for risk, actual market prices will vary from risk neutral prices and risk
neutral probabilities will vary from actual probabilites.
Because of this, the term risk-neutral probabilities (or risk-neutral
probability distribution) is used to refer to probabilities (or a distribution) which when used as weights in an
expected-value calculation will reproduce the market value of financial instruments. In
general, risk-neutral probabilities differ from real-world probabilities because the market does not assign value in the same way
that a risk-neutral individual would.
A far more mathematically advanced definition is "A risk neutral world is one where investors are assumed to require no extra
return on average for bearing risks"
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