In traditional finance and trading, Long and Short are the investment strategies that show a trader's prediction. Long means a trader is positive on the market, while Short means a trader is negative on the market. In terminology, they don't correspond directly to buy and sell.
Longning means predicting that the price of an underlying asset will go up.
Shorting is predicting that the price will go down. Shorting refers to selling an asset and rebuying it back at a lower price.
In cryptocurrency trading, Longning means buying Bitcoin or other digital currencies on an open market when you expect prices to increase over a reasonable period.
BTCMEX is a crypto derivatives exchange, that allows crypto investors to make a profit even if the BTC/USD price goes down by opening a Short position.
The cryptocurrencies market is highly volatile. Long and Short positions expand users' trading possibilities on the exchange.