DEFINITION of 'Contango'
A situation where the futures price of a commodity is above the expected future spot price. Contango refers to a situation where the future spot price is below the current price, and people are willing to pay more for a commodity
AT some point in the future than the actual expected price of the commodity. This may be due to people's desire to pay a premium to have the commodity in the future rather than paying the costs of storage and carry costs of buying the commodity today.
explication sur Investopedia :
http://www.investopedia.com/terms/c/contango.asp