What do long and short mean in trading?

A long earns when the price rises, a short earns when it falls. On perps both are opened the same way, with one click.

Going long means buying with the expectation that the price will rise. Going short means selling, betting on a fall. On perpetual futures you do not need to own the coin to short it.

The profit or loss of an open position is the unrealized PnL. With leverage, each position also has a liquidation price at which it will be closed by force.

On HyperScan

HyperScan shows the longs and shorts of every Hyperliquid whale and the overall long/short ratio of large traders for each coin.