To roll means to close or offset a position in one contract and open one in another expiry or series. In futures, the destination can be a more deferred month, not necessarily the immediately following one. Quantity, multiplier, notional, sensitivity and liquidity must be recalculated: keeping the same direction does not guarantee the same exposure.
The difference between the two contracts describes the curve; by itself, it is not an instant loss and is not the same as roll yield. Immediate costs are instead spread, commissions, slippage and possible risk between the two legs. For the procedure, dates and a numerical example, see Futures roll.
Sources
- U.S. Commodity Futures Trading Commission, Futures Glossary — Roll-Over.
- CME Group, Understanding Futures Expiration & Contract Roll.