It is also called a paper loss.
This is a loss that occurs as a result of the decline in the value of an asset. It can be applied to stocks, bonds, cryptocurrency, and even real estate. The term, however, is most often applied to financial markets.
It is also something that is reflected in people's brokerage or trading accounts.
The key here is the asset is still held. It is not sold, hence in the possession of the owner. This is contrasted with a realized loss which occurs when the asset is moved.
This is something that more are going to have to learn about as the prevalence of digital assets increases.