In contango, a futures contract costs more than the coin on the spot market, and contracts that expire further out cost more still. It is the normal state for Bitcoin and Ether: buyers pay extra to get exposure with leverage instead of tying up the full amount today.
The gap is called the basis. As expiry gets closer it shrinks, and on the expiry date the futures price meets the spot price. That lets traders earn the gap by buying the coin and selling futures at the same time (a "cash and carry" trade). In perpetual futures the same situation shows up as a positive funding rate.
A wide gap means traders are eager to bet on higher prices. In bull markets it can get very large, which is a sign of crowded, heavily leveraged long positions.
Bitcoin trades at $100,000 and the futures contract expiring in three months trades at $102,000. The $2,000 gap (about 8% a year) is contango.