So, let's assume that your starting account balance for a trade is $50, and you opened a position or you longed or shorted an asset but things started going wrong so much so that you were losing $5, because the trade was still running, your unrealized loss was $5 and the reason was because the trade was still running. The $5 loss could have also changed, things could have worsened and the loss could have grown to $5. 

In the same vein, you could be making some profits while the trade was still running, let's say at a point you were making $7, then that would be your unrealized profit. So,unrealized losses are losses on an open position based on the current market price and unrealized profits on the other hand, are gains on an open position based on the current market price 

What about realized profits and losses you may ask?.

Realized losses are losses from trading fees, funding fees and others for an open position or a trade you entered that have been settled on your account and realized profits are also gains that have been applied or settled on your account from similar sources.

When you open a trade, fees are charged, these fees are removed from your account balance and remember that we assumed an account balance of $50 earlier, so, say you were charged $0.01 for opening a position, this would be deducted from your $50, also, funding fees are calculated on certain intervals depending on the exchange and also applied on your account.

When a trade is running, unrealized profits or losses have noticeable impacts your account which means that your margin balance would reflect the magnitude of your gains or losses and this would also affect your equity if you are on the cross margin mode, because your margin balance is same as your equity since your entire account balance is used as collateral.