The keyword is decentralization.
A blockchain is nothing more than a database that is recorded at several nodes instead of at a central location.
This makes it possible to establish a relationship of trust between two parties for the exchange of values (money, securities, services, etc.) without needing a central location (bank, government, NGO, etc.).
But it’s cool.
Imagine, for example, having something that ANYONE can receive, own & send.
Without a central authority being able to take it away from you (e.g. through taxes or increasing the (money) supply)….
Blockchain brings all this and infinitely more.
Bitcoin runs on such a blockchain.
And Bitcoin can do exactly what is described above.
Ethereum now also runs on a blockchain, for example. You can program on it. DAPPS.