The difference between futures basis spreads and spreads.

1, The reference is different. The basis difference refers to the difference between the spot price of a particular commodity at a particular time and place and the futures price of that commodity in the futures market, i.e.: basis difference = spot price - futures price. The spread refers to the difference between the bid and offer prices of futures and is used as a measure of market liquidity. Under normal circumstances, the smaller the spread, the higher the liquidity. The spread is calculated by applying a position opening by subtracting the higher price side from the lower price side. Therefore, when opening a position, the spread is generally a positive number.

2, As both the futures price and the spot price are volatile, the basis spread is also volatile over the life of the futures contract. The uncertainty of the basis spread is known as basis risk. The key to reducing basis risk to achieve hedging is to choose a well-matched hedged futures contract. Basis risk is directly related to the basis spread at the time of hedge closeout. When an investor holds spot and holds a short position in futures to hedge, the investor will profit when the basis spread widens on the hedge closeout date. Conversely, when an investor will buy an asset in the future and holds a long futures position to hedge it, the investor will lose money as the basis spread widens on the hedge close date. And what is called a spread futures is said to be an arbitrage of futures.

There are also several classifications regarding arbitrage.
1, Spot and Futures Arbitrage: Arbitrage using the spread between futures and spot, which simply means that the spread between futures and spot is not at the normal level for the calendar period and will create room for arbitrage.

2, Cross-period arbitrage: the same species of different months of the contract price difference is not in the normal level of the existence of the difference is the space for arbitrage.

3, Cross-market arbitrage: the same variety of arbitrage on different exchanges is, in general, the use of a variety of abnormal spreads to earn profits.