The fact that it is a decentralised blockchain means that there is no central administrator, similar to how, for example, a bank has a central database. Instead, it can be seen as a network of identical databases that are either private or public. Private means that membership is limited. Public means that anyone with an internet connection has the opportunity to gain access. For cryptocurrencies such as Bitcoin, a private key and a public key are used. Everyone has access to the public key and can verify that a transaction is correct, but only the holder has access to the private key.