The difference between interest earned on a security posted as a loan’s collateral and the prevailing interest rate for loan collateral. More specifically, specialness measures the difference between the general collateral repo rate and the special collateral repo rate.

It reflects the ‘degree of specialness’ of the underlying security (e.g., a stock , a bond) used as collateral in the special repo. Positive specialness is seen as an indication of high market desirability or relatively limited supply of the stock collateral in the repo market.