Interest to fund the position, minus income received (dividends, yield), plus storage costs.
Each component pushes the forward in a predictable direction, which is why a dividend-rich index can have a forward below spot while a storable commodity has one well above.
Convenience yield is the commodity-specific term: a benefit to holding the physical asset now, behaving like a negative storage cost. It is what explains persistent backwardation in markets where physical availability matters.