Bitcoin (BTC) is the first and most famous cryptocurrency in the world, representing the following key points:
Decentralized currency: It is not governed by any central bank, government, or single financial institution. It is collectively managed by its network of users.
Blockchain technology: Bitcoin operates on the basis of "blockchain technology." It is a massive and distributed public ledger that permanently and transparently records all transactions in an immutable manner.
Mining: New bitcoins are "mined" and the network is protected by competitors (miners) who solve complex mathematical problems.
Total supply is limited: There will only ever be 21 million bitcoins, and this programmed scarcity is a key factor in its value.
