It is a risk associated with the refinancing of debt.
For example, the risk that an issuer of an obligation of short-term debt, could not sell new obligations of debt to shortly to obtain funds to pay the existing obligations.
Rollover risk occurs when the debt of countries and companies is about to mature and have to be rolled over into new debt.
If interest rates rise adversely, they would have to refinance their debt at a higher rate and incur more interest charges in the future.
The risk of refunding can be a manifestation of risk of liquidity or of risk of non-payment.