What is Basis Risk?

Legal Definition
Basis risk in finance is the risk associated with imperfect hedging. It arises because of the difference between the price of the asset to be hedged and the price of the asset serving as the hedge, or because of a mismatch between the expiration date of the hedge asset and the actual selling date of the asset (calendar basis risk), or—as in energy—due to the difference in the location of the asset to be hedged and the asset serving as the hedge (locational basis risk).
-- Wikipedia
Legal Definition
When risk changes interest rates causing a repricing. A mismatch in the assets liability is the result.