Trailing stop order is a more flexible variation of the normal stop order.
The trailing stop follows the market movements and adjusts the trigger price of the stop order accordingly.
Example: If the current price is 10000 USD for 1 BTC and you want to sell at 9000 USD for 1 BTC, but think the market will rise before it falls, you may set up a trailing stop. This means that the spread will be 1000 USD (the difference between current price and stop sell price). Therefore, if the price rises to 11000 USD for 1 BTC, your order will be repositioned to 10000 USD for 1 BTC, maintaining the spread. If the price then falls, your stop sell order will be executed at 10000 USD for 1 BTC.
Trailing stop orders are used for securing your profit and increasing the value of the order, following the profitable direction.