To be ‘short’ the market is taking a view that the value of an asset will fall. A short seller borrows said asset/securities via a margin account, on which they must pay fees/interest to the broker/dealer with whom they have the margin account. Said securities are then sold in the open market with the intention of buying the assets at a lower price than sold. This is a risky strategy as the reward is limited, (ie one’s gains are limited to the notional value of the original investment, ie the security falling to zero) whereby the downside is unlimited, ie the security can rise indefinitely. This is opposite of being ‘long’ an asset.