基差是同一资产的期货价格减去现货价格的差值，通常写作"期货价 − 现货价"。Basis is the difference between an asset's futures price and its spot price, typically expressed as futures minus spot.
基差为正，说明期货价高于现货（期货溢价）；为负，则是期货比现货便宜（折价）。它的大小和方向，反映了市场对这段时间内持有成本（资金、借贷、仓储等）的定价。基差走阔或收窄，说明现货与期货之间的关系在变化，套利者会盯着它寻找两个市场之间的定价偏差。A positive basis means futures are trading above spot (a premium); a negative one means futures are cheaper than spot (a discount). Its size and direction reflect how the market is pricing the cost of carrying the asset over time — financing, borrowing, or storage. When the basis widens or narrows, it signals a shift in the relationship between the spot and futures markets, and arbitrageurs watch it closely for pricing gaps between the two.