Also CTFF or cash-to-first futures. It is a short cash rate that is observed from current day to the maturity date of the first (nearest) futures contracts. This rate is derived when futures contracts are used for estimating the future LIBOR fixings in order to hedge a short-dated swap (a money market swap), which is usually done using a futures strip. This is often based on the assumption that the fixing take place on the start date of each period. However, that is not always the case, and hence it would be worthwhile to adjust calculation using the cash-to-first futures.