Capital gain
A capital gain is the positive difference between the sale price of an asset and its purchase price. It is realised that, at the moment, the asset is sold for a value higher than the one at which it was bought.
The concept applies to different types of assets, including financial instruments and crypto-assets. Until the asset is sold, any increase in value remains only potential (referred to in this case as an unrealised gain).
In many jurisdictions, capital gains are subject to taxation, with rules that vary by country and asset type. The tax treatment of crypto-assets depends on the applicable regulation and may change over time.
Disclaimer: This entry is for information purposes only and does not constitute tax or investment advice. For your specific situation, you should refer to official sources or to a professional.