An exception applicable during the Non-Call Period of an instrument (typically high yield bonds, but can also be included for certain loans), allowing the issuer or borrower to repay the debt in exchange for a significant prepayment penalty called Make-Whole Premium.
The calculation of the Make-Whole Premium is detailed in the debt documentation (bond indenture or loan credit agreement); the general principle is that the premium will be equivalent to the present value of all interest payments the issuer would have been liable to pay for the period between the intended early repayment date and the first date when the debt instrument becomes callable (ie the day when the Call Protection expires), discounted by the risk-free rate plus a premium (of generally 50bps).
See also: Non-Call Period, Call Premium