What it is:
An assignable contract allows a contract holder to assign his or her rights and obligations under the contract to a third party. The most common assignable contracts are futures contracts.
How it works (Example):
Let's assume you own a futures contract to buy corn at a certain price in the future, and the value of the contract has increased by $10,000 since you bought it. Because futures contracts are often assignable, you can sell the contract to a third party today in return for cash, and the third party then assumes all the rights, responsibilities, and financial outcome of the contract from that point forward.
Not all futures contracts are assignable, especially those traded on exchanges.