Scarcity refers to the limited availability of a resource or item. In the context of digital currencies, scarcity is achieved through the use of blockchain technology and the limited supply of coins. For example, Bitcoin has a fixed supply of 21 million coins, which ensures that there will never be more than 21 million bitcoins in circulation.

The use of blockchain technology solves the "double-spend problem," which is the challenge of ensuring that digital money cannot be easily duplicated or spent twice. By creating a decentralized ledger that records all transactions, the blockchain ensures that the supply of bitcoins is limited and that each coin can only be spent once. This scarcity helps to maintain the value of the currency and to prevent inflation.

In conclusion, scarcity is an important aspect of digital currencies and is achieved through the use of blockchain technology and limited coin supplies. It helps to ensure the integrity of the currency and to maintain its value over time.