A blockchain is a database. It stores data. Specifically, it’s a database designed for storing cryptocurrency transactions, such as “Alice sends 10 bitcoins to Bob. Signed: Alice”, or what is commonly called a ledger. Now, this is a simple transaction, but a blockchain may store more complex ones, such as conditional transactions, calls to smart contract functions, or just for storing data.
What makes it different from a standard database?
Well, first of all, anyone can write to a blockchain. There are no permissions, no limitations, no identified users. The only rule for writing data to a blockchain is that a new transaction including a digital signature is needed to move a record from one owner to another.
In order to sign a transaction, a user needs a private key, which is a piece of cryptographic information typically stored in a digital wallet.
Are blockchains going to replace current databases?
Certainly not. They have severe limits and disadvantages: blockchains are very slow and inefficient; each transaction has to include a fee, paid by the sender; and all the information stored in a blockchain is public, which may be considered a liability, especially in corporate environments. But blockchains do solve a host of issues with current storage systems, and we believe their usage will increase tremendously over the coming years.