Kerry Back
The forward curve shows the prices of contracts for different delivery dates.
It shifts up and down over time as prices change.
Its slope can also change.
The front month price is the “spot price” - i.e., the price for (near) immediate delivery.
\[\text{spot}\! =\! \frac{\text{futures}}{(1+r)^6} \; \Leftrightarrow \; \text{futures} \!=\! \text{spot}\! \times\! (1+r)^6\]
A market is in contango if the forward curve is upward sloping, as in the gold example.
In other words, you pay more for future delivery than in the spot market.
The term originates from deferring purchase of a stock. You had to pay a fee to postpone settlement.
Contango is natural, because of the time value of money. But, there are other factors.