Blockchain is a time-stamped series of immutable data records, managed by a network of computers, which are not owned by any single entity. Each of these blocks of data (block) is secured and bound to each other using cryptographic principles (chain).
The blockchain network has no central authority - it is the very definition of a democratised system. Since it is a shared and immutable ledger, the information in it is open for anyone and everyone to see. Hence, anything that is built on the blockchain is, by its very nature, transparent and everyone involved is accountable for their actions.
This helpful video explains it all, in just two minutes.