Traders can go short at the bid price.
The terminology is from the broker point of view, they are bidding to buy from you.
Other Trading Basics
Backwardation occurs when a bid price exceeds the ask price.
This usually occurs when stock is suspended or under a share repurchase scheme.
It can also mean that a futures contract will trade at a higher price when it is coming close to expiring.
The opposite of backwardation is known as contango.
Learn the skills needed to trade the markets on our Trading for Beginners course.