Impermanent loss is the temporary reduction in value that liquidity pool providers experience when the price ratio of their deposited token pair changes compared to when they deposited. The greater the price divergence, the larger the impermanent loss. It is called "impermanent" because the loss only becomes permanent if the provider withdraws their funds while the prices are still diverged. If prices return to the original ratio, the loss disappears.
Impermanent Loss
Impermanent Loss Explainer Video
What is Impermanent Loss? | Crypto Terms Explained