If you buy a share at 50 dollars and it now trades at 70, you have an unrealized gain of 20 dollars per share. It becomes realized only when you sell. Until then, the profit exists on paper and can disappear if the price falls. The same applies to losses.
Companies report them too. A firm that holds shares or other investments may need to record changes in their market value, and these can swing net income from one quarter to the next without any change in its main business. Large technology companies with big stakes in other firms often show this effect.
These items can make earnings harder to read. A strong quarter may owe much of its profit to a rise in an investment's value, which may reverse later and says little about operating performance.
Separate such gains and losses from core results, check the notes for the investments involved and focus on operating income.