Unrealized Profit / Loss represents an increase/decrease in the value of an open position. Unrealized P/L is a reflection of what profit or loss could be realized if the position were closed at that specific time. P&L does not become realized until the position is actually closed.
For example, you open Long Position for 1 BTC at the BTC price of $9,000. If the next day BTC price is $9,100, your unrealized gain is $100.
But it may be too early to celebrate. The price may take a nosedive and drop to $8,500 by the end of the day. Since your position remained open, you are now in for $500 loss ($9,000 - $8,500).
Yet still, the loss is not your final verdict unless you actually close your position. If in two days BTC price recovers to $9,050 and you close the position, you finally turn your unrealized gain into realized of $50.